Refining Management Strategies for Common Squid (Todarodes pacificus) Fishing Vessel Fisheries in Korean Waters

Abstract

This study develops integrated bioeconomic management strategies for the common squid (Todarodes pacificus) fishery in Korea’s coastal waters, addressing both biological conservation and economic sustainability amid severe stock depletion and declining fishery profitability. Drawing on recent catch data and cost structures for six Total allowable Catch (TAC)-managed fishery types, common squid-specific economic indicators were estimated using a stepwise cost allocation method. Based on previous research using the Catch—Maximum Sustainable Yield (CMSY) model with limited Catch Per Unit Effort (CPUE) data, the biomass in 2020 was estimated at approximately 56% of Biomass at Maximum Sustainable Yield (BMSY), indicating an overfished state. Scenario-based simulations identified TAC allocation thresholds at which net profits reach zero, providing a benchmark for adaptive quota redistribution. Results show variation in economic sensitivity and common squid dependency among fishery types: common squid-dependent gears such as offshore jigging and East Sea trawl exhibit high vulnerability, while multi-species fisheries such as purse seine remain resilient. These results provide a basis for developing tailored management strategies for each fishery, thereby enhancing the effectiveness of interventions. Accordingly, policy recommendations include dynamic TAC adjustments, expanded monitoring, introduction of an Individual Transferable Quota system, and coordinated stock assessments with China and Japan. These findings contribute to refining Korea’s TAC system by aligning stock recovery goals with the economic viability of fishing operations.

1. Introduction

The production trend of common squid (Todarodes pacificus) in Korea’s coastal waters peaked at 250,000 tons in 1996, remained at approximately 200,000 tons until the mid-2000s, and continuously decreased thereafter. In 2024, the official statistics show a production of 13,000 tons, the lowest figure on record, representing a 94.6% reduction compared to the highest yield year of 1996 and a 42% reduction compared to the previous year (Figure 1). The common squid is commercially important and ranks among the most preferred seafood species in Korea. In a 2022 survey of Korean perceptions of seafood, for three consecutive years, Korean respondents selected common squid as their favorite seafood [1].

Korea manages common squid stocks through regulations such as TAC, closure periods, length limits, prohibition of joint operations between trawlers and jiggers, and light power limits in fishing. Among these regulations, the TAC has the most direct impact. There are six fishery types targeting common squid: pair trawl, offshore jigging, offshore gill net, trawl, purse seine, and East Sea trawl [3]. However, despite the implementation of various management tools aimed at stock recovery, the yield of common squid in Korea’s coastal waters continues to decline, and associated management challenges persist.

Accordingly, this study aimed to identify the management status of the six types of fisheries subject to TAC, with the common squid as the main target species, and to propose a more effective quota system by integrating biological and economic considerations. Meanwhile, depleted stocks not only reduce biological yield but also raise marginal harvesting costs, reinforcing the need for integrated biological and economic thresholds in TAC design [4]. In particular, dependency on a single species can amplify the economic risks faced by fishers, while sensitivity to cost changes influences their operational resilience under fluctuating market and stock conditions [5]. Therefore, based on CMSY analysis reflecting the declining stock size, the study suggests reducing the total TAC and reallocating it efficiently using net profit thresholds through an ITQ framework, thereby enabling economically viable vessels to acquire additional quotas from others. In other words, the economic thresholds proposed here—particularly the break-even point—are derived under biologically constrained scenarios to ensure compatibility with sustainable exploitation principles. Furthermore, this study compares the common squid dependency and economic sensitivity across fishery types and proposes tailored management strategies that account for the operational characteristics of each sector.

2. Materials and Methods

This study applied scenario-based analyses of vessel-level TAC quotas to identify the threshold level of common squid (Todarodes pacificus) landings at which net profit becomes zero. This threshold was then used as a reference point for reallocating TAC among fishery types.

Net profit of common squid for each fishery type was estimated as the difference between the ex-vessel price and production cost. However, most fisheries harvest multiple species in addition to common squid, requiring a procedure to isolate the squid-specific ex-vessel price and production cost. To address this, a stepwise estimation approach was employed to allocate costs and revenues specifically to common squid and calculate net profit per ton by fishery type. The data sources and methodology are outlined below.

2.1. Materials

This study analyzed six fishery types that are subject to Korea’s Total Allowable Catch (TAC) system and primarily target the common squid (Todarodes pacificus). These fishery types include pair trawl, offshore jigging, offshore gill net, trawl, purse seine, and East Sea trawl. To evaluate economic and policy implications, this research utilized two data intervals: a three-year period (2021–2023) and a five-year period (2019–2023). Although extended time series are generally preferred for economic analyses, the recent sharp decline in common squid landings required a narrower window to reflect current conditions.

The economic assessment incorporates five major indicators. The ex-vessel price, defined as the unit price fishers receive upon landing their catch at port, includes both operational costs and profit margins from Statistics Korea. Production costs, including fuel, labor, and gear, were obtained from the fisheries business survey report [6,7,8,9,10] published by the Cooperatives Fisheries Economic Research Institute. Net profit per ton was calculated by subtracting the production cost from the ex-vessel price. The number of fishing vessels (both registered and TAC-participating) was retrieved from Statistics Korea and the Korea Fisheries Resources Agency (FIRA), while annual catch data were sourced from Statistics Korea.

2.2. Methods

A stepwise economic estimation method was employed to calculate net profit per ton of common squid for each fishery. Each vessel’s production cost for common squid was derived by allocating its total production cost across all target species, proportionally to the share of common squid, as shown in

Table 1. Per-vessel production costs estimated by incorporating the common squid cost distribution rate into the total fishery costs (Unit: 1 USD, %).

Fishery Type	Average (2021–2023)			Average (2019–2023)
	Total Cost	Common Squid		Total Cost	Common Squid
		Ratio (%)	Cost		Ratio (%)	Cost
Pair trawl	3,200,139	(35.7)	1,142,449	3,103,645	(35.1)	1,089,379
Offshore jigging	310,874	(64.8)	201,447	310,019	(68.5)	212,363
Offshore gill net	753,029	(12.7)	95,635	721,564	(10.2)	73,599
Trawl	1,578,826	(36.2)	571,535	1,809,019	(47.8)	864,711
Purse seine	10,676,349	(0.1)	10,676	9,967,884	(0.1)	9968
East Sea trawl	486,575	(77.6)	377,582	655,251	(84.4)	553,032

. Per-vessel average yield was calculated by dividing the total common squid yield by the number of vessels. Production cost per ton was calculated by dividing the per-vessel common squid production cost by the average common squid catch (tons) per-vessel. Net profit per ton was calculated as the difference between the ex-vessel price and the unit production cost, and the equation is as follows.

Production cost per-vessel:

$$C_{v,s}=C_{v,all}\times \left({\displaystyle \frac{Q_s}{Q_{all}}}\right)$$

(1)

where C_v,s is the squid-specific production cost per-vessel, C_v,all is the total production cost for all species per-vessel, and ${\displaystyle \frac{Q_s}{Q_{all}}}$ represents the share of common squid in total yield.

Per-vessel average yield (tons):

$${\bar{Q}}_{v,s}={\displaystyle \frac{Q_s}{N}}$$

(2)

where ${\bar{Q}}_{v,s}$ is the average squid catch per vessel (tons), Q_s is the total squid catch, and N is the number of vessels.

Production cost per ton:

$$C_{ton}={\displaystyle \frac{C_{v,s}}{{\bar{Q}}_{v,s}}}$$

(3)

Net profit per ton:

$${\pi }_{ton}=P_{ton}-C_{ton}$$

(4)

where π_ton is the net profit per ton, P_ton is the ex-vessel price per ton, and C_ton is the production cost per ton.

Second, for each fishery type, we examined changes in production costs by applying scenarios that increased or decreased the TAC quotas based on the production costs per -vessel. Reducing the TAC quota is necessary to support stock recovery, as both catch volume and estimated biomass of common squid have declined, indicating an overexploited stock status. However, given the need to balance stock recovery with fishery management viability, both quota increase and decrease scenarios were applied to find a reference point for the TAC quota that considers both stock and management. Accordingly, an analysis was conducted to determine how profitability would change depending on the scenario in which each fishery type’s TAC quota was increased (+) or decreased (–) at the TAC quota and target vessel levels for the 2024–2025 fishing season (2024.7–2025.6).

Based on the simulation results, the study proposes an efficient management strategy for common squid in Korea’s coastal waters, taking into account the sustainability and operational characteristics of each fishery.

3. Ecological and Managerial Background of Common Squid Fisheries in Korea

3.1. The Ecological Status of the Common Squid

Todarodes pacificus, which inhabits the waters surrounding Korea, belongs to the Teuthoidea Ommastrephidae of the class Cephalopoda. As shown in Figure 2, it is a migratory fish species distributed in areas including Korea, the East China Sea, Hong Kong, Japan, and the Kuril Islands, inhabiting depths from the surface down to 100 m. It spawns during winter (January to March), summer (June to August), and fall (September to November) [11]. Among the winter, summer, and fall spawning groups, the fall spawning group occurs in the Southeast and Northeast China Seas from October to December. The Tsushima Current carries most into the East Sea, becoming Korea’s primary target of common squid fishing [12]. The Japanese common squid (Todarodes pacificus) is recognized as an economically important species with an annual life span, and its population dynamics are strongly affected by climatic and environmental variability [13]. As an annual species, the continued decline in common squid catch is directly linked depletion.

Adult common squid first rest on the sea bottom and then ascend to spawn in surface waters above the thermocline. The egg masses, being denser than the surrounding water, sink to a stable buoyancy depth above the thermocline. After hatching, juveniles rise to the surface and are carried by currents to feeding grounds (Figure 3) [14].

The primary fishing methods for catching common squid in Korea are offshore jigging, gill nets, and pair trawls. Offshore gill nets and trawls are fishing types that are widely known around the world, and Figure 4 is a schematic diagram illustrating the fishing types of offshore jigging and pair trawls, which are commonly used in Korea. Pair trawl is a type of fishery where two fishing vessels work together by towing fishing gear. At the same time, offshore jigging is a type of fishing that utilizes the tendency of common squid to be attracted to light by installing fishing lights such as metal halide lamps, and catching them using electrically driven automatic squid jigging machines [17].

3.2. Common Squid Resource Evaluation Results by Prevalent Research

3.2.1. Stock Assessment of Korean Standard Square Using BSS (Bayesian State-Space) Model [18]

From 2000 to 2018, the total catch of common squid and the Catch Per Unit Effort (CPUE) for three fishing types (trawl, offshore jigging, purse seine) were used as the basis for the BSS model in conducting a stock assessment. The results show that for common squid, the intrinsic growth rate (r) is 1.02, the carrying capacity (K) is 1,151,259 tons, the Maximum Sustainable Yield (MSY) is 293,421 tons, and the B_MSY used to estimate MSY is 575,629 tons, as estimated. Common squid stock has been showing a continued declining trend in recent years, and in 2017 the stock volume was 443,911 tons, which was evaluated to be lower than the B_MSY level. Moreover, by comparing and analyzing the results of resource assessments when considering multiple fisheries and when independently considering only a single fishery, the necessity of resource assessments that consider multiple fisheries was demonstrated.

However, data from neighboring countries cannot be utilized without considering the migratory characteristics of the common squid found in the surrounding seas of Korea. Additionally, there is a limitation in that the data from before 2000 cannot be used.

3.2.2. Stock Assessment of Uroteuthis Chinensis in the Northeastern South China Sea Using the Length-Based Bayesian Biomass Estimation (LBB) Method [19]

A stock assessment was conducted on Uroteuthis chinensis using the LBB method, which relies on length frequency data collected from 1975–1977, 1997–1999, and 2018–2019. The assessment revealed that the length of Uroteuthis chinensis in 2018–2019 was smaller than in previous years, indicating increased fishing pressure. The B/B_MSY ratio estimated for 1975–1977 was 2.8, significantly higher than the B/B_MSY values recorded for 1997–1999 and 2018–2019. Furthermore, in 2018, fishing power (measured in horsepower) increased to nearly four times the sustainable level, and it was noted that overfishing began in the mid-1980s. Reducing catch amounts and establishing regulations on catch sizes are essential to restoring resources.

3.2.3. Stock Assessment of Common Squid in Korea, China, and Japan Using CMSY Model [20]

The common squid migrates through the waters surrounding Korea and utilizes the waters of Korea, Japan, and China. Previous research evaluated the common squid resources of the three countries, considering their migration patterns in the seas around Korea. Due to the unavailability of CPUE data from each country, this study employed the CMSY (Catch-Maximum Sustainable Yield) model, a catch-based stock assessment method using Monte Carlo simulation. The CMSY model has been increasingly used in recent studies, as it enables stock assessments even in the absence of effort data, making it suitable for species with limited CPUE information [21,22,23]. However, due to the difficulty in collecting data from third countries, there is a limitation in ensuring continuous updates. This suggests the need to share information with neighboring countries for migratory species. As shown in

Table 2. Assessment of common squid stock status in Korea, China, and Japan, using the CMSY model.

B2020	BMSY	B2020/BMSY (Stock Status)
932,342	1,673,498	0.56
(81,765–1,327,303)	(1,258,725–2,224,945)	(Overfished)

, the stock was estimated at approximately 930,000 tons in 2020, which corresponds to about 56% of B_MSY, leading to the assessment of the stock status as ‘Overfished’.

Figure 5 shows the estimated Kobe plot generated using the CMSY model. If the value on the X-axis is greater than 1, the stock exceeds B_MSY, whereas a value below 1 indicates that the stock is less than B_MSY. For the Y-axis, a value greater than 1 means that F_MSY is excessive, while a value below 1 indicates that F_MSY is at an appropriate or lower level. In terms of color classification, green represents a healthy state, yellow indicates a recoverable state, orange signifies a state at risk of overfishing, and red represents the most critical state. As of 2020, the probability that the common squid stock shared by Korea, China, and Japan falls within the yellow (overfished but not overfishing) zone is 59.8%, while the probability of being in the red (overfished and overfishing) zone is 39.5%. In other words, the common squid stock has significantly decreased. Currently, the catch volume continues to show a decreasing trend, and considering that the common squid is an annual species, one of its main ecological characteristics is that effective resource management for the common squid is necessary.

3.3. Current Status of Common Squid Production and TAC Management

Figure 6 shows the basic status of common squid, presenting each fishery type’s catch and TAC management status. This shows the 2024 catch scale of common squid by fishery type, indicating that common squid is produced the most among TAC-targeted fishery types, except for the fixed-net fishery—62.9% of total common squid landings were from fishery types subject to TAC. In particular, among the TAC fishery types, offshore jigging, offshore gill net, and pair trawl account for 60% of the total yield of the fishery.

Figure 7 shows each fishery type’s TAC consumption rate of common squid. In the 2022–2023 fishing season (July 2022–June 2023), the overall consumption rate was 31.8%, whereas the minimum and maximum consumption rates among each fishery type were 6.2% and 79.6%, respectively. The total consumption rate for the 2023–2024 fishing season (July 2023–June 2024) was 24.0%, and each fishery type’s minimum and maximum consumption rates were 0.7% and 75.5%, respectively. As such, the overall TAC consumption rate for common squid remains low, driven by declining stock levels, and it is evident that there are large variations in consumption rates among fishery types. This outcome highlights the need for a more adaptive and responsive adjustment of total TAC allocations. Although CPUE has declined, some fisheries such as purse seine maintain profitability due to multi-species targeting. In contrast, common squid-dependent fisheries like offshore jigging and East Sea trawl have shown negative profits in recent years, leading many fishers to forgo fishing trips to reduce operating expenses. The number of fishing days has been decreasing every year. In particular, in 2024, the East Sea trawl recorded a significant drop to 59.1% compared to the previous year, while offshore jigging decreased by 14.1% from the previous year [10]. Despite same target species, TAC quota consumption rates vary significantly between fishery types, indicating inefficiencies in quota allocation and the necessity for a more adaptive distribution system.

4. Analysis Result

4.1. The Outcomes of the Net Value Analysis of Common Squid by Each Fishery Type

To analyze the production cost per ton for each fishery type, the total production costs per vessel for common squid were divided by the yield per vessel. When calculating the production cost per vessel, the number of vessels varies significantly depending on whether it is based on the TAC target and TAC operation fishing vessels or on the permitted fishing vessels [23]. Therefore, all three criteria were applied, and the net profit was ultimately analyzed to determine which standard produced the most meaningful results. When applying the three different vessel count criteria [24,25,26,27,28], 2021–2023, and 2019–2023 statistics were used. As a result, as shown in

Table 3. The estimated production cost per ton for each fishery type on a per-vessel basis (Average for 2021–2023) (Unit: 1 USD, Ton).

Fishery Type	2021–2023 Average
	Common Squid		Production Cost Per Ton (Based on the Number of Fishing Vessels)
	Per Vessel Production Costs	Per Vessel Average Yield (Tons)	TAC Target	TAC Operation	Permit
Pair trawl	1,142,449	515.1	2218	2218	2218
Offshore jigging	201,447	24.5	7952	6327	8231
Offshore gill net	95,635	12.5	7519	5003	7678
Trawl	571,535	122.8	5394	4883	4656
Purse seine 1	10,676	7.1	1389	1389	1493
East Sea trawl	377,582	91.5	3727	3487	4128

¹ The proportion of common squid fisheries for each fishery type was calculated by applying the common squid cost distribution rate to the total fish species ex-vessel price. However, for the purse seine fishery, the actual squid yield is very low at 0.1%, but its ex-vessel price is relatively high, resulting in a cost distribution rate of 7.7%. Due to such extreme discrepancies and the resulting understatement of costs, the yield proportion (0.1%) was applied.

and

Table 4. The estimated production cost per ton for each fishery type on a per-vessel basis (Average for 2019–2023) (Unit: 1 USD, Ton).

Fishery Type	2019–2023 Average
	Common Squid		Production Cost per Ton (Based on the Number of Fishing Vessels)
	Per Vessel Production Costs	Per Vessel Average Yield (Tons)	TAC Target	TAC Operation	Permit
Pair trawl	1,089,379	505.9	2153	2153	2153
Offshore jigging	212,363	30.4	6993	5730	6993
Offshore gill Net	73,599	11.4	6073	4196	6441
Trawl	864,711	162.3	6369	5589	5329
Purse seine	9968	9.2	1047	1012	1088
East Sea trawl	553,032	112.0	4456	4169	4936

, the cost of producing one ton of common squid for each fishery type was estimated for 2021–2023 and 2019–2023.

4.2. Net Profits Analysis Results per Vessel for the Common Squid Fishery

When production amounts and production costs based on the number of fishing vessels are applied for three or five years, the value closest to the business profit from fishing in

Table 5. Fishing business profits from the East Sea trawl and offshore jigging fisheries [6,7,8,9,10] (Unit: 1 USD).

Fishery Type	2021–2023 Average	2019–2023 Average
East Sea trawl	49,463	103,072
Offshore jigging	−944	13,141

is estimated to be the most reliable net profit. Business profit from fishing includes all fish species produced by each fishery type. The proportion of common squid catch is high for the two fishery types in Table 5, making them comparable. The condition for comparison is that net profits are analyzed as positive (+). Although the recent offshore jigging fishery business profit from fishing in 2021–2023 showed a negative (−) value, we did not take a negative net profit into account. While accounting principles accept losses, this study uses the zero-profit threshold as a policy benchmark. The ‘break-even’ point defines the TAC level where fisheries become unsustainable, avoiding assumptions beyond current data.

To analyze the net profits produced annually by a single vessel, simulations were conducted for each scenario based on production amount, costs, number of boats, and the period used for statistics. Then, the most suitable figures were identified by comparing the results with Table 5. The results showed that using three years from 2021 to 2023 and employing the registered number of vessels, as in

Table 6. Estimated per-vessel production costs and net profits for common squid by fishery types subject to TAC (Unit: 1 USD).

Fishery Type Catch	Annual Average Per Vessel in 2021–2023		Based on Yearly Squid Production Per-Vessel
	Catch (Ton)	Ex-Vessel Price	Production Cost		Net Profits
			Per Ton	Total
Pair trawl	480	2,575,307	2218	1,064,859	1,150,448
Offshore jigging	25	223,530	8231	208,512	15,019
Offshore gill net	12	103,938	7678	95,634	8304
Trawl	123	673,786	4656	571,536	102,250
Purse seine	7	24,288	1493	10,775	13,514
East Sea trawl	92	426,584	4128	377,935	48,631

, yielded the most appropriate outcomes for each scenario analyzed. While it is generally beneficial to use statistical data from as many years as possible, the stark decline in common squid yield in recent years meant that longer-term statistics did not adequately reflect current conditions. The unit production cost per ton, shown in Table 3, is based on the permitted standard values. The total production cost was calculated by multiplying the unit cost by the average catch volume for the period 2021–2023. Net profits were derived by subtracting the production cost from the ex-vessel price. Given that net profit was estimated using aggregated data, the standard deviation (SD) could not be calculated and was therefore omitted from the analysis.

4.3. Results of TAC Quota Analysis of Production Cost Levels

The analysis in

Table 7. Estimated ex-vessel prices based on the TAC quota decrease ratio (Unit: 1000 USD).

Fishery Type	Per-Vessels Production Costs	Ex-Vessel Prices Based on the TAC Quota Increase and Decrease Ratios
		5%	−50%	−60%	−75%	−95%
Pair trawl	1065.0	1057.1	503.4	402.7	352.4	50.4
Offshore jigging	208.5	417.4	198.8	158.9	139.1	19.8
Offshore gill net	95.4	95.8	45.6	36.4	31.9	4.5
Trawl	571.8	1799.7	856.9	685.5	599.9	85.7
Purse seine	10.4	237.3	113.0	90.4	79.1	11.3
East Sea trawl	377.7	1041.8	496.0	396.8	347.3	49.6

applies the TAC quota of increasing and decreasing ratios for each fishery type to the annual average (2021–2023 fishing seasons) common squid production costs per-vessel, by fishery type, subject to the common squid TAC. The TAC quota ratio was analyzed for each scenario from plus (+) 5% to minus (–) 95%, and the result closest to the annual production costs per-vessel was considered the point where net profits become zero. The TAC allocation reduction percentage where net profit becomes zero by fishery type was 5% for pair trawl and 5% for offshore gill net, −50% for the offshore jigging, −60% for East Sea trawl, −75% for trawl, −95% for purse seine fishery. In other words, allocating TAC quotas more equitably by cost levels and TAC quota utilization performance is necessary. These results served as the foundation for the management strategies proposed in Section 5, highlighting the need for quota reallocation tailored to economic viability.

Figure 8 presents a comparative chart classifying the six fishery types participating in the TAC program into five levels each for economic sensitivity and common squid dependency, based on the analysis conducted in this study. Offshore jigging showed high sensitivity in both indicators, while the East Sea trawl exhibited both economic sensitivity and high common squid dependency. Pair trawl and offshore gill net fisheries, which target multiple species, had relatively low common squid dependency but very high economic sensitivity. Trawl and purse seine fisheries scored low on both indicators, with the purse seine fishery showing the lowest levels in particular, as it primarily targets large catches of chub mackerel (Scomber japonicus). These findings can be used to develop tailored strategies for each fishery type.

4.4. Discussion

If the TAC allocation reduction rate at which net profit reaches zero in Table 7 is positive, it indicates that additional TAC allocation is required, suggesting higher economic sensitivity compared to other fishery types. Conversely, a negative threshold implies lower sensitivity. Accordingly, by comparing the break-even TAC thresholds between the 2020–2021 and 2021–2023 fishing seasons, changes in economic sensitivity can be estimated. According to the analysis of the 2020–2021 fishing seasons based on previous research, the TAC allocation reduction percentage at which net profit becomes zero by fishery type was −10% for pair trawl, −25% for East Sea trawl, −30% for offshore jigging, 35% for trawl, −45% for offshore gill net, and −80% for purse seine fisheries [20].

Comparing the results of the 2020–2021 fishing seasons from previous studies with those of the 2021–2023 fishing seasons in this study, the offshore gill net fishery showed the greatest increase in sensitivity followed by pair trawl, which was consistent in both seasons. The purse seine fishery exhibited almost no change and remained the least sensitive, likely because common squid is a bycatch species in this fishery. In contrast, fisheries targeting common squid as a primary species—offshore jigging, trawl, and East Sea trawl—showed reduced sensitivity, with thresholds shifting from −30% to −50%, −35% to −70%, and −25% to −60%, respectively. Although offshore jigging, trawl and East Sea trawl fisheries showed relatively lower sensitivity in this analysis, it is important to note that these are the primary fisheries targeting common squid. This reduction in sensitivity is likely attributable to the withdrawal of an increasing number of vessels in recent years, as operators sought to minimize operating costs under declining stock conditions and unfavorable markets. Therefore, the need for TAC reduction and reallocation remains valid, particularly to ensure that quota distribution reflects both biological realities and the economic viability of active vessels.

These findings align with previous research in demonstrating the economic vulnerability of common squid-dependent fisheries under declining stock conditions. Moreover, while earlier assessments using models such as BSS or CMSY emphasized the overfished status of common squid, the present study further contextualizes these biological findings within a fishery-specific economic framework. This allows for a more policy-relevant understanding of how TAC adjustments should be tailored to each fishery’s operational viability and stock dependence. Furthermore, future research should incorporate climate change impacts and transboundary cooperation mechanisms, as these external factors critically influence the sustainability of common squid fisheries.

In this study, the method used to estimate net profit was based on the approach applied in the author’s doctoral dissertation, updated using the recent cost structure (2019–2023) [20].

5. Common Squid Stock Management Strategy

The TAC quota decrease ratio at which net profits become zero (0) varies greatly by each fishery type for common squid TAC target fisheries. To address these disparities, there is a need for more efficient quota allocation management between the different common squid TAC target fishery types. Additionally, it is necessary to properly distribute the TAC quota and establish a system that allows the transfer of TAC quota between fishery types. Accordingly, institutional and financial policy improvements have been proposed to manage the common squid stock more effectively.

First, expanding the fishery types included in the TAC target is necessary to assess the status of the common squid stock more accurately and manage it effectively. By closely monitoring fishing activities—such as gear selectivity, fishing grounds, and catches by season—it is necessary to apply TAC or designate landing ports for fishery types not currently included under the TAC system and to manage them accordingly. In parallel, stricter enforcement of TAC regulations should be accompanied by an expansion of monitoring efforts—particularly across a broader range of species—to ensure that bycatch and non-target catches are effectively tracked and managed. Additionally, incorporating biodiversity-based indicator species selection methods [29] into TAC planning could improve alignment between stock management and ecosystem health. This integrated approach will contribute to more systematic and ecologically sound resource management.

Second, the total TAC volume needs to be adjusted to reflect the recent level of catches and the ongoing decline in stock abundance. Given the sharp annual decrease in catch and the consistently low quota utilization rates, the current TAC volume appears to be unrealistic. One possible reason is the continued reliance on multi-year historical statistics as the basis for TAC determination. Therefore, it is necessary to adopt a more dynamic and responsive approach to setting TAC volumes that better reflect current conditions.

Third, since the quota consumption rate for TAC differs by each fishery type and season, introducing an ITQ (Individual Transferable Quota) system is needed to manage the remaining TAC quota more efficiently. If catches are poor, transferring quotas to vessels with higher quarterly consumption can help ensure net profits. In particular, since there are significant catch differences among common squid fishery types, the ITQ system would contribute to more stable fishing operations. Depending on the fishing situation, some of the total TAC could be reserved for public auction or the purchase of fishermen’s TAC quota to be used as financial resources for more efficient operation of business stability and TAC-target stock management. However, the paper acknowledges the need for further analysis of equity and social implications before implementation.

Fourth, improving the current method of allocating common squid TAC quota is necessary. Considering stock status, reducing the quota might be unavoidable, and such reductions should be appropriately allocated based on the management conditions of each fishery type. Reviewing the allocation using the management evaluation data derived from this study makes it possible to assign appropriate TAC amounts without reducing net profits. However, a sharp reduction in the exclusive TAC quota would likely meet resistance in the field. Therefore, the TAC should be decreased gradually; for unused quotas, the government should consider establishing funds to purchase them.

Fifth, efforts need to be made to transition to other fishery types and to reduce the number of fishing vessels further. One good way to restore fishery resources and maintain sustainable fisheries is to minimize catch per unit. Therefore, switching from existing offshore jigging to other fishery types is essential for further reducing the number of vessels to lower the catch per unit.

Sixth, developing and supplying more advanced equipment to further modernize existing fishing methods and reduce operating costs is necessary. To reduce labor costs, which account for the most significant cost in vessel operation, it is necessary to develop and disseminate automated fishing and processing equipment and develop and supply standardized hull forms, catch equipment, or engine facilities that can save fuel.

Finally, there is a need to share relevant statistics and to carry out joint stock assessments for the common squid stocks with China and Japan, which share the surrounding waters with Korea. Given the extensive migration routes of common squid across the surrounding waters and the rapidly changing climate issues, a coordinated response by Korea, China, and Japan is necessary to address current uncertainties.

Some of these improvement measures were developed using insights from the author’s doctoral dissertation, and this study further added strategies tailored to the characteristics of each vessel type [18].

Among the previously presented management strategies for common squid, the expansion of TAC-covered fisheries and strengthened monitoring, reduction of the total TAC and reallocation of quotas, introduction of the ITQ system, and joint stock assessments among Korea, China, and Japan are strategies applicable across all fisheries. Other strategies—such as reducing the number of vessels, converting fishing license types, expanding fishing grounds, modernizing fishing equipment, and developing cost-efficient gear and engines (R&D)—should be applied in accordance with the operational conditions of each fishery type. To this end, based on the economic sensitivity and common squid dependency identified in Figure 8 and the advantages and disadvantages examined in this study, tailored policy development is supported as shown in

Table 8. Advantages, disadvantages, and tailored strategies by fishery type.

Fishery Type	Advantages	Disadvantages	Strategies
Pair trawl	Relatively stable catch performance	Increased production costs due to fuel and labor expenses from two-vessel paired operations	Modernization of cost-efficient fishing equipment and engine development (R&D)
Offshore jigging	High selectivity, single-species targeting	Declining profitability, reduced operations	Reduction in the number of vessels, conversion of fishing license types
Offshore gill net	Diverse species selectivity, flexible deployment	Highly sensitive to cost changes	Modernization of fishing equipment
Trawl	High operational efficiency, decreased economic sensitivity	High dependency on common squid relative to fishing efficiency	Reduction in the number of vessels
Purse seine	Large-scale catch potential, minimal impact on common squid resources	-	Monitoring of fishing operations
East Sea trawl	High productivity	Limited fishing grounds, dependency on common squid stock	Reduction in the number of vessels, expansion of fishing grounds

.

6. Conclusions

This study sought efficient TAC management measures to solve the problems of stock reduction and business deterioration in each fishery type for the common squid, a major species caught in Korea’s coastal waters. In particular, focusing on the six fishery types participating in TAC, the study quantitatively analyzed production costs, net profits, and TAC decrease scenarios, and presented response measures that reflect the management realities of the fisheries. The results of this study showed that the TAC reduction level at which net profits for each fishery type become zero (0) and the sensitivity to cost increases varied by type. Fishery types such as offshore jigging, which are highly sensitive to cost increases, experienced a rapid decline in profitability, even with a slight rise in external costs. However, some types, such as purse seine fisheries, showed no significant difficulty maintaining profitability. These findings highlighted the need for effective allocation of TAC quotas. In addition, the study presented various policy alternatives, such as establishing TAC redistribution criteria based on net profit analysis, reviewing the necessity of the ITQ system, vessel capacity reduction, conversion strategies for fishery types, and the development of new fishing grounds.

For future improvement of this study, it is necessary to conduct quantitative simulation research on the acceptability and effectiveness of introducing the ITQ system and sensitivity analysis reflecting the impact of external variables such as climate change and rising fuel costs on fishery management. In addition, this study was limited in its ability to capture price elasticity and market uncertainty. Future research should incorporate more detailed sensitivity analysis that accounts for changing market conditions and their potential impacts on fisheries management and economic viability.

Finally, this study is significant in that it proposes an integrated management plan that can enhance the effectiveness of the common squid TAC system and simultaneously ensure both stock management and the livelihoods of fishermen, thereby making a policy contribution.