Introduction
The Patagonian toothfish (Dissostichus eleginoides Smitt, 1898) is a circumpolar species endemic to the southern hemisphere. Its distribution in the Pacific Ocean includes Ecuadorian waters (Aramayo, Reference Aramayo2016; Zambrano et al., Reference Zambrano, Coello and Herrera2023a). The main method of fishing for D. eleginoides, a commercially important species, is the deep-sea longline technique, which involves placing baited hooks near the seabed (Collins et al., Reference Collins, Brickle, Brown, Belchier and Lesser2010).
Experimental fishing of D. eleginoides began in Chile in 1955, but significant catches were not made until the late 1960s (Moreno, Reference Moreno1991). The Peruvian fishery began in 1995 with the purchase of two vessels from Chile. Commercially important catches have been made since 1996 (Sancho-Andrade, Reference Sancho-Andrade, Sancho-Andrade, Ortiz -Von Halle and Naranjo-Cuvi2002).
During the period 2017–2021, one fishing vessel conducted experimental fishing for D. eleginoides in Ecuador. The results reported that the bycatch by number of individuals consisted of the following: fish (52%), skates and rays (23%), sharks (15%), crustaceans (6%), and cephalopods (4%). Antimora rostrata, Centroscymnus owstonii, Coryphaenoides armatus, C. delsolari, Etmopterus granulosus, and Hydrolagus melanophasma were the most abundant bycatch species (Sepa et al., Reference Sepa, Coello, Herrera and Zambrano2022; Zambrano et al., Reference Zambrano, Coello and Herrera2023a, Reference Zambrano, Coello and Herrera2024b).
The Food and Agriculture Organization (FAO) has reported that levels of exploitation of D. eleginoides populations are unsustainable (FAO, 2024). On the other hand, according to the FAO’s categorization, one stock is at its maximum sustainable level, while five are under-exploited (Sharma et al., Reference Sharma, Barange, Agostini, Barros, Gutiérrez, Vasconcellos, Fernández-reguera, Tiffay and Levontin2025). In Chile, this fishery is currently under-exploited. However, there is a risk of overexploitation under the incipient development or recovery regime (which is managed with special fishing permits), and it is already overexploited under the closed access regime (Subsecretaria de Pesca y Acuicultura, 2024); meanwhile, the biomass of D. eleginoides in Peru is showing signs of recovery (IMARPE, 2024).
Experimental fishing for D. eleginoides was carried out in Ecuador for 5 years; however, the effect that this had on the population is unknown. The study aimed to assess the sustainability of the D. eleginoides experimental fishery in Ecuadorian waters using length-related indicators as a tool for fishery management.
Materials and methods
The Public Institute for Aquaculture and Fisheries Research provided the database related to the D. eleginoides experimental fishery, which took place between July 2017 and December 2021. Only one fishing vessel carried out fishing activities within Ecuador’s exclusive economic zone, which was divided into three areas: Area I (1°28′ N–0°00′), Area II (0°00′–2°00′ S), and Area III (2°00′–3°23′ S) (Figure 1).
Fishing sites (grey circles) and study areas of the experimental fishery of Patagonian toothfish (D. eleginoides) in Ecuadorian waters. Taken and modified from Zambrano et al., (Reference Zambrano, Coello and Herrera2023a).
Figure 1 Long description
The map displays fishing sites and study areas for the experimental fishery of Patagonian toothfish in Ecuadorian waters. The map is divided into three areas: Area I, Area II and Area III. Gray circles represent fishing sites distributed along the coast of Ecuador. Area I is located between 1°28′ N and 0°00′, Area II between 0°00′ and 2°00′ S and Area III between 2°00′ and 3°23′ S. An inset map shows the location of Ecuador relative to Colombia and Peru, with the Pacific Ocean labeled. The scale is 1 to 2,400,000 and a compass rose is included for orientation. The map provides geographic coordinates along the borders, with latitude and longitude marked. The distribution of fishing sites appears to follow a linear pattern along the coast within the defined areas.
Data on D. eleginoides were recorded by observers on board for all individuals caught. These included total length (TL), total weight (TW), sex, and maturity status (immature or mature). The number of hooks, coordinates, and depth were also recorded for each fishing site. Monthly fishing trips lasted between 8 and 18 days. Bottom longlines with 500–1,500 circular hooks (No. 14/0) were used for fishing. These were set at depths between 1,000 and 2,500 m (Sepa et al., Reference Sepa, Coello, Herrera and Zambrano2022; Zambrano et al., Reference Zambrano, Coello and Herrera2023a, Reference Zambrano, Coello and Herrera2024b).
Analysis of variance and Dunn’s post hoc test with Bonferroni’s adjustment method were used to compare the mean lengths of D. eleginoides between areas, depths, and years. The biological reference points were the length at sexual maturity (L 50) and the recruitment length (L r). For females, L 50 = 117 cm TL (Oyarzún et al., Reference Oyarzún, Gacitúa, Araya, Cubillos, Galleguillos, Pino, Aedo, Salamanca, Pedraza and Lamilla2003), whereas for males, L 50 = 103 cm TL (the minimum length recorded in mature individuals), because almost all the individuals were adult males.
Recruitment lengths were 98.7 cm TL in females and 87 cm TL in males. Recruitment was defined as the size at which fish become available to the fisheries and may involve their arrival in the fishing area (Lorenzen and Camp, Reference Lorenzen and Camp2019).
We assumed that the selection curve for fishing gear is the same as the recruitment curve (Sparre and Venema, Reference Sparre and Venema1997). The lengths of premature individuals were between L 50 and L r. Sustainability indicators for lengths were based on the proportional stock density (Gabelhouse, Reference Gabelhouse1984) and corresponded to the proportion (%) of adult, premature, and recruit individuals, by year and fishing area. The analyses were performed by sex and differentiated by area, depth, and year. The length-frequency distributions were represented using violin plots in Stata software, version 16.0 (Jann, Reference Jann2022).
Length-based indicators (LBIs) were applied according to sex (Table 1). The TL was grouped into 5 cm intervals, and the sum of TW in each size class was added. The m/k ratio established was 1.5. The reference points and expected values proposed by the International Council for the Exploration of the Sea were used (ICES, 2015; Kell et al., Reference Kell, Minto and Gerritsen2022). The analysis was run using the LBI application (https://scott.shinyapps.io/LBIndicator_shiny/). Asymptotic length (L inf) was 176.24 cm LT for both sexes (Oyarzún et al., Reference Oyarzún, Gacitúa, Araya, Cubillos, Galleguillos, Pino, Aedo, Salamanca, Pedraza and Lamilla2003).
Length-based indicators (LBIs), calculation, reference points, expected values, and properties, applied to the experimental fishery of Patagonian toothfish (D. eleginoides), in Ecuadorian waters
Table 1 Long description
Length-based indicators define reference points and target thresholds for assessing the Patagonian toothfish fishery using size composition. Two conservation checks focus on avoiding immature catch: length at first catch and the 25th percentile length are each compared with maturity length, with targets above maturity. A second conservation check compares the mean length of the largest 5 percent with asymptotic length, targeting more than 0.8 to retain large individuals. The proportion of very large fish is assessed as the share above the optimal length plus 10 percent, with a reference range of 0.3 to 0.4 and a target above 0.3. Two yield-oriented indicators use mean length of fish above the first-catch length: one compares it with an optimal-length reference and expects a ratio close to 1, and another compares it with a fishing-length reference and expects at least 1. The table lists expected directions and properties but does not provide observed values, so performance against these targets cannot be determined from this information alone.
Taken from ICES (2015).
Results
A total of 5,265 were collected: 4,195 females, 843 males, and 227 unidentified individuals. The sex ratio was 5:1, and the average length was 128.1 cm TL in males and 136.5 cm TL in females. Females showed the smallest mean length in 2017 (132.4 cm TL) and the largest in 2021 (144.7 cm TL). Males had the smallest average lengths in 2017 and 2018 (124 cm TL). Significant differences in mean length were observed between years (p < 0.05) for both sexes. For females, only 2019 presented a mean length similar to 2017, 2018, and 2020, while in males, 2017 and 2018 showed a mean length comparable to 2019 and 2021.
Significant differences were found according to fishing area for both sexes (p < 0.05), except for males in Areas I and II where the difference in mean length was not significant (p > 0.05). Area III had the largest mean lengths, but less data were available for this area. In terms of depth, significant differences (p < 0.05) in mean length were only observed between the 1,000–1,499 and 1,500–1,999 categories. It should be noted that the 2,000–2,499 category had the least amount of data (Table 2).
Number of individuals (n), minimum, maximum, mean, and confidence intervals of the total length (TL) of Patagonian toothfish (D. eleginoides) caught in Ecuadorian waters by year, area, and depth
Table 2 Long description
Patagonian toothfish total length in centimeters is summarized by sex across years, fishing areas, and depth bands, reporting sample size, minimum and maximum length, mean length, and 95 percent confidence intervals. Females had larger samples and longer mean lengths than males in every breakdown. Female mean length increased over time from 132.4 cm in 2017 to 144.7 cm in 2021, while male means rose more modestly from 124.8 cm to 132.5 cm. By area, mean length was highest in Area III for both sexes, at 141.8 cm for females and 136.5 cm for males, compared with lower means in Areas I and II. By depth, females were longest on average at 2,000 to 2,499 m with a mean of 138.0 cm, while males were longest at 1,000 to 1,499 m with a mean of 127.8 cm. Length ranges were wide, with female minima down to 71.0 cm and maxima up to 193.0 cm, and male minima down to 77.0 cm and maxima up to 182.0 cm. Confidence intervals are narrow where sample sizes are large and wider in the deepest band, especially for males, so depth comparisons at 2,000 to 2,499 m are less precise.
Most individuals collected were adults, regardless of year, area, or sex. The proportion of adults was ≥76% among females but was higher among males (>87%). In Area III, only adults were found. Recruits were scarce or absent (<15%), particularly among males. On the other hand, the proportion of premature individuals was ≤21% in females and ≤10% in males (Table 3).
Number (n) and percentage (%) of Patagonian toothfish (D. eleginoides) caught in Ecuadorian waters by developmental stage
Table 3 Long description
Counts and percentages of Patagonian toothfish caught in Ecuadorian waters are broken down by area, year from 2017 to 2021, sex, and developmental stage (adult, premature, recruit). Adult fish make up the clear majority in every area and year for both sexes: females range from 76.0 percent adults (Area II, 2017) up to 93.1 percent (Area III, 2021), while males are typically 93 percent or higher and reach 100 percent in all Area III years and in Area I during 2021. Premature females are the main non-adult component, peaking at 21.3 percent in Area II during 2017, while premature males stay low, generally between 0 and 10.3 percent. Recruits are uncommon throughout: female recruits are usually at or below 3.5 percent, and male recruits are mostly zero with small exceptions such as 1.1 percent in Area I during 2020 and 12.5 percent in Area II during 2021 (based on a small count). Total counts across all areas and years are 3,472 adult females, 645 premature females, 78 female recruits, 793 adult males, 45 premature males, and 5 male recruits. Percentages are within each area-year-sex group, so comparisons should consider that some years have much smaller sample sizes, especially for males in Area I during 2021 and females in Area III during 2018.
Length frequency distributions were similar for both sexes. The highest mean length was observed in 2021; however, the number of individuals decreased from 2015 onwards. The highest catches were observed at depths between 1,500 and 1,999 m, as well as in Areas I and II. In all cases, most individuals exceeded the size at sexual maturity and recruitment (Figure 2).
Total length distribution (cm) of Patagonian toothfish (D. eleginoides), from the experimental fishery in Ecuadorian waters, by sex, years (2017–2021), depth (A, 1,000–1,499 m; B, 1,500–1,999 m; C, 1,500–2,499 m), and fishing zones (I, II, and III). Solid line represents recruitment size (L r), and segmented line shows the size at sexual maturity (L 50).
Figure 2 Long description
The figure title text reads: Total lengths distribution (cm) of Patagonian toothfish. Three groups of violin plots show total lengths by sex under three category sets. All plots share the same y-axis label, Total lengths (cm), with tick labels 50, 70, 90, 110, 130, 150, 170, 190, 210. Each violin contains an internal box and a central marker. Each plot includes two horizontal reference lines: one solid and one dashed. The image A showing year categories for Females and for Males. The x-axis categories are 2017, 2018, 2019, 2020, 2021. For Females, five violins appear, one per year, with central markers around the 120 to 140 range on the y-axis. For Males, five violins appear, one per year, with central markers around the 100 to 120 range on the y-axis. The solid and dashed reference lines run across both the Females and Males year plots. The image B showing depth categories for Females and for Males. The x-axis categories are A, B, C. For Females, three violins appear, with the B category having the widest violin shape among A, B and C. For Males, three violins appear, with narrower violins than the Females depth plot. The solid and dashed reference lines run across both the Females and Males depth plots. The image C showing zone categories for Females and for Males. The x-axis categories are I, II, III. For Females, three violins appear with central markers around the 120 to 140 range on the y-axis. For Males, three violins appear with central markers around the 100 to 120 range on the y-axis. The solid and dashed reference lines run across both the Females and Males zone plots.
Over the last 3 years of fishing, the LBI has consistently remained above the reference points for conservation, optimal yield, and maximum sustainable yield (MSY), for both sexes. The exception was L c/L mat for females; the values were ≤1 in 2019 and 2020. The indicators: L c, L 25%, L mean, and MSY showed ratio values ≥1.04, while for P mega and L max5% were >0.5 and 0.9, respectively. Females presented higher values for the indicator ratio L mean/L opt and males in the ratio L 25%/L mat (Table 4).
Indicator status for the most recent 3 years in the Patagonian toothfish (D. eleginoides), from the experimental fishery in Ecuadorian waters
Table 4 Long description
Indicator ratios for Patagonian toothfish are listed by sex for 2019, 2020, and 2021 across conservation, yield optimization, and MSY-related measures. For females, Lc to Lmat is 0.92 in 2019 and 1.00 in 2020 (both flagged as below the reference), then rises to 1.09 in 2021; other female indicators are consistently above their reference levels, including Pmega increasing from 0.62 to 0.78 and Lmean to Lopt rising from 1.17 to 1.29. For males, Lc to Lmat stays above the reference in all years (1.09 in 2019, 1.04 in 2020 and 2021), while Pmega ranges from 0.51 to 0.59. L25% to Lmat is above the reference for both sexes each year, reaching 1.13 for females and 1.19 for males in 2021. Lmax 5% to Linf is above the reference for females (0.97 to 1.03) but remains below it for males (0.91 to 0.92). Overall, 2021 shows the highest values for most indicators, and females tend to have higher ratios than males, but interpretation should note that some values are explicitly marked as below the reference level.
* Values under the reference level. MSY, maximum sustainable yield. Expected values are in brackets.
Discussion
In Ecuador, experimental fishing for D. eleginoides consisted mainly of female individuals (83.1%), a pattern also observed in sub-Antarctic waters. Between 1997 and 2021, 54% of females were reported at South Georgia Island. In 1996, the highest proportion of females was reported at depths greater than 1,200 m. For the period 2006–2009, the female proportion at Banzare Bank was between 63% and 72% (Sancho-Andrade, Reference Sancho-Andrade, Sancho-Andrade, Ortiz -Von Halle and Naranjo-Cuvi2002; Taki et al., Reference Taki, Kiyota, Ichii and Iwami2011; Abreu et al., Reference Abreu, Hollyman, Xavier, Bamford, Phillips and Collins2024). By contrast, the proportion of males reported in Chilean waters in 2006 was 65.3% for longline fishing (Guerrero and Arana, Reference Guerrero and Arana2009). Therefore, the D. eleginoides fishery in Ecuadorian waters (the most northern of its distribution) showed the highest proportion of females compared to other referenced fisheries.
The movement patterns of D. eleginoides are variable. They may either remain within a range of 20 nm for a long period of time (ca. 7 years) or travel long distances (400 nm) within the same period (Troccoli et al., Reference Troccoli, Martínez, Di Marco, Waessle and Wöhler2023). Considering the sex ratio of D. eleginoides females and the movement patterns of the species, we assume that the female concentrations increase towards the northern part of their distribution range, while males predominantly remain in Chilean waters.
The females of D. eleginoides in Ecuadorian waters are larger than the males, as is the case in other fishing areas. Between 2006 and 2009, the lengths reported at Banzare Bank were 110.6–114.7 cm TL for females and 97.5–106.3 cm TL for males (Taki et al., Reference Taki, Kiyota, Ichii and Iwami2011). In Chilean waters, modal lengths ranged between 70 and 75 cm TL in 2001–2002. In 2006, the values were 103.1 cm TL for males and 108.8 cm TL for females. In 2014, the range was 93–114 cm TL (Oyarzún et al., Reference Oyarzún, Gacitúa, Araya, Cubillos, Galleguillos, Pino, Aedo, Salamanca, Pedraza and Lamilla2003; Guerrero and Arana, Reference Guerrero and Arana2009; Céspedes et al., Reference Céspedes, Vargas and Adasme2016). The average lengths observed in Peruvian waters were 108.3 cm TL and 110.1 cm TL for 2023 and 2024, respectively (IMARPE, 2024).
The average length of D. eleginoides increases towards the equator, but the largest individuals are found at higher latitudes within each country (Oyarzún et al., Reference Oyarzún, Gacitúa, Araya, Cubillos, Galleguillos, Pino, Aedo, Salamanca, Pedraza and Lamilla2003; Céspedes et al., Reference Céspedes, Vargas and Adasme2016). On the other hand, larger lengths have been reported at greater depths, such as in South Georgia Island. In Argentina, the average length increased to 92 cm TL between 2001 and 2003, due to fishing at depths of over 800 m (Sancho-Andrade, Reference Sancho-Andrade, Sancho-Andrade, Ortiz -Von Halle and Naranjo-Cuvi2002; Martínez and Wöhler, Reference Martínez and Wöhler2016). Therefore, the variation in the lengths of D. eleginoides is related to its geographical distribution and movement patterns, as well as stratification at depth.
The D. eleginoides individuals collected in Ecuadorian waters were mostly adults, indicating that the experimental fishing had avoided recruitment overfishing and that future levels of spawning stock biomass would remain sustainable (Mace, Reference Mace1994; Myers, Reference Myers1994; Ben-Hasan et al., Reference Ben-Hasan, Walters, Hordyk, Christensen and Al-husaini2021). In this sense, the LBIs demonstrated adequate levels of conservation/sustainability, yield optimization, and MSY. While stocks of D. eleginoides in Antarctic and sub-Antarctic waters are reported to be overfished and at their MSY (although some remain underfished), there are signs of recovery in Peruvian waters (FAO, 2024; IMARPE, 2024; Sharma et al., Reference Sharma, Barange, Agostini, Barros, Gutiérrez, Vasconcellos, Fernández-reguera, Tiffay and Levontin2025).
For the period 2007–2012, Ecuador was ranked 17th among countries importing/exporting D. eleginoides and 9th among exporters alone. During this time, the catch weighed 2,750,950 kg, but this species was not the fishing target (Grilly et al., Reference Grilly, Reid, Lenel and Jabour2015). In the period 2017–2021, a single vessel conducted experimental fishing in Ecuadorian waters, catching 137,762 kg of D. eleginoides. However, the annual catch decreased from 34,419 kg at the beginning of the period to 17,339 kg in the last year (Zambrano et al., Reference Zambrano, Coello and Herrera2023a).
A similar scenario was observed in South Georgia, where both the annual catch and catch per unit effort fluctuated. Catches decreased between 1997 and 2021 but have remained stable since 2011 due to strict management measures being adopted (Abreu et al., Reference Abreu, Hollyman, Xavier, Bamford, Phillips and Collins2024). Experimental fishing for D. eleginoides revealed a healthy population consisting primarily of adult females. However, if it becomes an open fishery, strict regulations must be implemented regarding fleet size, gear type, and fishing depth. Furthermore, the population status of D. eleginoides should be evaluated using robust methods to enable adaptive fisheries management and the sustainable use of the resource.
Acknowledgements
The paper is based on the Master’s thesis of V. M. V.-C. The author is grateful to the Public Institute of Aquaculture Research and Fisheries (IPIAP, its Spanish acronym) for permission to use the data (IPIAP-GCT-2022-0036-OF). The data were part of the project ‘Distribution, abundance, and biological aspects of Patagonian toothfish (Dissostichus eleginoides) in Ecuadorian oceanic waters’ supported by IPIAP and TRANSMARINA C.A. The authors would like to thank René Zambrano for the review and suggestions.
Author contributions
V. M. V.-C.: Definition, conceptualization, methodology, formal analysis, writing – original draft, writing – review & editing, and visualization. J. C. M.-P.: Definition, conceptualization, and methodology. M. H.: Definition, conceptualization, project administration, and funding acquisition.
Declaration of interest
The authors declare none.
Data availability statement
The data that support the findings of this study are available from the Public Institute of Aquaculture Research and Fishery. Restrictions apply to the availability of these data, which were used under license for this study. Data are available from M. H. with the permission of the Public Institute of Aquaculture Research and Fishery.
Funding statement
This research received no specific grant from any funding agency, commercial, or not-for-profit sectors.
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