Instantaneous Total Mortality Research Articles

Estimates on age, growth, and mortality of Leuciscus chuanchicus (Kessler 1876) in the Ningxia section of the upper reaches of the Yellow River, China

To investigate the age structure, growth pattern, mortality and exploitation rates of Leuciscus chuanchicus in the upstream Ningxia section of the Yellow River, four sampling surveys were conducted between 2022 and 2023. A total of 472 individuals were measured for their total length (TL) and body weight (W). Age determination was performed using otoliths. The collected samples had a range of total lengths from 4.52 to 37.45 cm, body weights ranging from 0.68 to 552.43 g, and ages ranging from 1 to 7 years old. The relationship between total length and body weight was expressed as W = 0.0052 L3.19 for all samples, which indicates that the growth of L. chuanchicus adheres to allometry. The Von Bertalanffy growth equation revealed that the fish had an asymptotic total length (L∞) of approximately 37.9 cm with a growth coefficient (K) value of approximately 0.461 yr−1. Using the age-based catch curve method, the calculated total instantaneous mortality rate (Z) for all samples was determined as being equal to approximately 1.1302 yr−1. Additionally, three methods were used to estimate the average instantaneous rate of natural mortality (M), resulting in an approximate value of 0.7167 yr−1 for all samples. Furthermore, the instantaneous rate of fishing mortality (F) for all samples was calculated as 0.4134 yr−1, leading us to determine that the exploitation rate (E) is 0.3658. It was concluded that the growth rate of L. chuanchicus in the upstream of the Yellow River is relatively fast, and L. chuanchicus has not been subjected to excessive exploitation, yet its relatively high natural mortality rate underscores the need for targeted management measures aimed at preserving its habitat.

Population dynamics and stock assessment of Queenfish (Scomberoides commersonnianus) from the marine waters of Bangladesh

AbstractThe Queenfish, Scomberoides commersonnianus, is a large commercial fish in Bangladesh. This is the first study on the Queenfish that aims to elucidate life history parameters and stock status to suggest authority for sustainable management and to support future research on this economically significant species in the region. We used three length‐based approaches to establish a standard for sustainable management of the fishery: (1) TropFishR to give the growth parameters and current exploitation status, (2) the length‐based Bayesian biomass estimation (LBB) to quantify stock biomass, (3) and Froese's sustainability indicators (LBI). The length–weight relationship of Queenfish was a negative allometric pattern (b = 2.84; R2 = 0.98). Growth parameters for Queenfish were L∞ = 124.22 cm, K = 0.31 year−1. Instantaneous total mortality Z = 0.71 year−1, instantaneous natural mortality M = 0.36 year−1, and instantaneous fishing mortality F = 0.35 year−1. Based on the LBB approach, the current estimated stock biomass was overexploited (B/BMSY = 0.65). We recommend strictly maintaining mesh size of nets to reduce harvest of immature fish shorter than 62 cm, while focusing harvest on fish 62–74 cm, to minimise recruitment and growth overfishing.

The management of common carp fisheries using spawning potential ratio in the southeast of the Caspian Sea

AbstractSpawning potential ratio (SPR) is an important index used by fisheries biologists and managers to determine how a fishery should be harvested to prevent recruitment overfishing. In the southeastern Caspian Sea, Iran, 3430 common carp Cyprinus carpio were caught by beach seine in 2‐week intervals of two fishing seasons in 2019 and 2020. Fork length (FL) was measured to the nearest 1 cm. The age and maturity stage of 434 specimens, including 236 females and 198 males, were estimated by scale and gonad microscopic examinations. Estimated L∞ was 71.9 and K (growth constant) was 0.09. Instantaneous total mortality (Z) was 1.08, natural mortality (M) was 0.18, and fishing mortality (F) was 0.9. Estimated SPR at current fishing mortality (0.18) was lower than the reference point (0.4). Our findings indicated that fishing mortality should be reduced to F = 0.38 for C. carpio to meet the SPR reference point of 0.4. Further, higher minimum length limits should be set to reduce fishing mortality, and catch quotas for fishing cooperative corporations should be considered to meet the 40% SPR threshold.

Estimates of the Age, Growth, and Mortality of Triplophysa scleroptera (Herzenstein, 1888) in the Upper Reaches of the Yellow River, China

To investigate the age composition, growth pattern, mortality, and exploitation rate of Triplophysa scleroptera in the upper reaches of the Yellow River, we measured the total length (L) and body weight (W) of 347 individuals based on three sampling surveys from 2022 to 2023. The otoliths were used in this investigation to determine age. The total length of the collected samples ranged from 5.69 cm to 18.40 cm, body weight ranged from 1.65 g to 50.22 g, and the age ranged from 1 to 7 years old. The relationship of total length and body weight was W=0.009L2.942 for the total samples, and the growth pattern observed in the study belongs to the isometric type. The von Bertalanffy growth equation revealed that the fish had an asymptotic total length L∞ of 37.536 cm, and the growth coefficient K was 0.064 yr−1. Total instantaneous mortality rate (Z) of total samples calculated by the age-based catch curve method was 1.092 yr−1. The average instantaneous rate of the natural mortality (M), estimated by three different methods, for the total samples was 0.237 yr−1. The instantaneous rate of fishing mortality (F) for the total samples was calculated as 0.855 yr−1, and the exploitation rate (E) was determined as 0.783. As a whole, compared with other Triplophysa fishes, the growth rate of T. scleroptera in the upper reaches of the Yellow River is relatively slow, and the population of T. scleroptera has been overexploited. It is crucial to establish some effective management strategies to protect this species.

Estimates of adult Lake Trout mortality fromcoded wiretags in a population with developing natural reproduction in southern Lake Michigan

AbstractObjectiveOverfishing and Sea LampreyPetromyzon marinuspredation led to extirpation of Lake TroutSalvelinus namaycushfrom Lake Michigan in the 1950s. Large populations of hatchery‐reared fish were developed by the 1970s, but natural reproduction was limited until the early 2000s when it began to increase in the southern main basin. Hypothesizing that the relatively low mortality of spawning‐aged fish contributed to this reproductive success, we estimated the total annual mortality rate for this population.MethodsWe used catch curves to estimate the total instantaneous mortality rateZusing coded wire tags, which provided definitive ages. We made separate estimates from fish collected in three on‐going surveys: a spring gill‐net survey, a fall gill‐net spawning survey, and a sport fishery survey.ResultOur estimates ofZ ± SE were 0.297 ± 0.019, 0.239 ± 0.009, and 0.205 ± 0.007 for the spring, spawning, and sport fishery surveys, respectively. We suggest that the meanZ ± SE of all survey estimates of 0.247 ± 0.027 would be a reasonable estimate for this population, which equates to a total annual mortality of 22 ± 3%. This estimate is in the low range of rates reported for the species and is in the same range as other populations in the Great Lakes with well‐established natural reproduction.ConclusionWe concluded that these low total mortality rates contributed to the reproductive success in southern Lake Michigan through increasing spawning stock density and age structure and that previous estimates of another important population parameter, the instantaneous natural mortality rateM, were too high. Estimates ofMranged from 0.210 to 0.240 and were based on the Pauly equation, a growth‐ and temperature‐based estimator. We suggest maximum‐age‐based estimators ofMare more appropriate for Lake Trout. Several alternative maximum‐age‐based estimators produced estimates forMof 0.132–0.058, all of which are more compatible with our estimate ofZ.

A generalized application of the catch-curve regression with comparisons of adult mortality and year-class strength between hatchery-stocked and wild-reared lake trout in US waters of Lake Huron

The recently developed approach to estimating the instantaneous total mortality of coded-wire-tagged lake trout ( Salvelinus namaycush) is generally applicable to catch-at-age data. We further formalized the technique to objectively incorporate the year-class and year effects into the model structure of catch-curve regression. We used this new method to compare adult mortality and year-class strength between the hatchery-stocked and wild-reared lake trout in US waters of Lake Huron, one of the Laurentian Great Lakes. Model comparisons showed no difference in adult mortality between the hatchery-stocked and wild-reared lake trout. Based on 95% confidence intervals, the estimate of adult mortality using the simple catch-curve regression with average number-at-age was not statistically different from the estimate using the linear mixed model with individual number-at-age of multiple year-classes and sampling years. The linear mixed model, however, also quantified lake trout year-class strength and indicated that since 2003, the increases in recruitment of wild-reared lake trout did not fully compensate for the rapid declines in recruitment of hatchery-stocked lake trout in Lake Huron.

River- and Sex-Specific Annual Survival Rates of Mature Anadromous Alewife (Alosa pseudoharengus)

During multiple annual spawning runs from 2013 to 2021, over 9,000 mature anadromous alewife (Alosa pseudoharengus A. Wilson, 1811) were monitored with passive integrated transponders (PITs) in four rivers of the Chignecto Isthmus, Bay of Fundy, Canada. A subsample of 384 individuals tagged during 2016–2019 were aged from 3 to 6 years (mean ± SD; 4.2 ± 0.7 years, n = 232, males; 4.5 ± 0.7 years, n = 152, females). Biotelemetry revealed that one unsexed individual survived seven years post tagging, possibly making it 10–13 years old. Return rates varied among the rivers, with the lowest rates in the most anthropogenically impacted river. Biotelemetry and ageing data were used to estimate apparent annual survival rates ranging from 0.25 to 0.50 depending on the river and the year. Based on capture-mark-recapture (CMR) analysis of biotelemetry data from the three less impacted rivers, the estimated overall annual survival was 0.396, total instantaneous mortality (Z) was 0.93, and future life expectancy from time of release was 1.08 years. Frequency distribution of ages 4–6 for alewife pooled from all four study rivers estimated a lower annual survival rate of 0.301, Z = 1.20, and a future life expectancy of 0.83 years. The biotelemetry detection rates were 0.89–0.98 but varied depending on the river and the year, with the lowest rates in one river during 2017-2018 possibly related to a malfunctioning tide gate preventing upstream fish passage and subsequent detection. Based on CMR, males had a higher survival rate compared to females, which translated into an overall mean survival increase of 0.05. Alewife survivorship in our study highlighted that a limited ecosystem-based management period is required to mitigate river connectivity and mortality issues to avoid loss of population cohorts and decrease the risk of extirpation.

Applying a novel state-space stock assessment framework using a fisheries-dependent index of fishing mortality

State-space models have a hierarchical framework that assumes the observed data are derived from a time series of unobserved latent states. State-space stock assessment models have emerged as an alternative framework to conduct stock assessment in Canada, the east coast of the United States of America, and in Europe though little research has investigated where and how they are optimally used and if they would be appropriate in other geographical contexts. We built a novel state-space stock assessment model with process variation in recruitment and time- and age- specific catchability. We fit the model to commercial trap net and gill net catch and effort data of Lake Michigan lake whitefish using a marginal likelihood that integrated over latent states. Compared to the previously employed statistical catch at age model, the state-space model estimated dome-shaped, rather than asymptotic selectivity for both fisheries, 15% lower average total instantaneous mortality, and 20% higher average recruitment. To our knowledge this is the first application of a state-space stock assessment model fit by maximum likelihood in the Laurentian Great Lakes and the first such model to not include a fisheries-independent survey. These results demonstrate the feasibility of employing a maximum likelihood state-space framework in fisheries that lack such fishery independent indices of abundance and instead use catch per unit effort as an index of abundance. This work presents a novel approach to applying state-space stock assessment modeling and offers insights and suggestions for future use in the Great Lakes and in similar circumstances of data availability.

Assessment of Stock Status, Metal Contents with Human Health Risk of Gudusia chapra from Oxbow lake, Bangladesh

The current study is focused on a comprehensive stock assessment of Gudusia chapra to assess the stock status along with feeding habits, essential minerals content and risk to human health from exposure to heavy metals. A total of 723 specimens from the Bukvora Baor, Bangladesh were used to estimate the total body length (TL) and body weight (W) which ranged from 5.5 to 14.5 cm and 1.62–26.45 g, respectively. The estimated asymptotic length (L∞) of this species (15.38) was in comparison with average length at 10 cm from 723 specimens along with the rate of 0.70 yr−1 for approaching to asymptotic length. The obtained growth performance index (φ) 2.2 indicates that this species is not economically feasible to bring under aquaculture. At an average annual water surface temperature of 28 °C, natural mortality, 1.71yr−1 indicating good ecological suitability of Bukvora oxbow lake (Baor). The estimated current exploitation ratio (0.24) reflected under-exploitation status with total instantaneous mortality (2.25 years−1) and fishing mortality (0.55 years−1). The recruitment pattern of this species was observed across the year, with main peak occurring during the period of April to May. The estimated total steady state biomass (3.91 metric ton) and MSY (4.40 metric ton) based on length-structured virtual population analysis (VPA) length-structured virtual population analysis (VPA) through FiSAT II schedule indicating the sustainable production of this species. The obtained values of proximate compositions (% of protein, fat, Moisture, ash) showed no significant variations during different seasons throughout the year. The monthly measurements of GaSI showed significant alterations (p < 0.05). The value of essential minerals (Na and Ca) was recorded 9.18 mg and 245.19 mg per 100 g of fish flesh, respectively. Target hazard quotient and Cancer risk for all detected heavy metals were far below the recommended levels by United States Environmental Protection Agency. Therefore, the target fish species from oxbow lake is safe and have no human health risk. Therefore, the outcomes of this research would be very worthwhile in carrying out specific management for G. chapra in Baor ecosystems.

Reduced lifetime fitness (growth, body condition and survivability) of hatchery-reared tiger pufferfish Takifugu rubripes compared to wild counterparts.

Tiger pufferfish Takifugu rubripes (order Tetraodontiformes, family Tetraodontidae) is a highly exploited species and stocks continue to decline, although hatchery-reared juveniles have been released since 1965 for stock enhancement. To determine why the stock has not recovered through hatchery-release practices, this study investigated and compared the population characteristics of wild and hatchery-origin fish. The length-mass relationship showed that hatchery-origin fish were skinnier, with males weighing less than 90% of the mass of wild males of the same length. The hepatosomatic index tended to be lower in hatchery-origin fish. Age was estimated using the otolith-based method, and the estimates were more accurate and precise than those obtained by the conventional vertebra-based method. At the age of 2.9 years, an age at which specimens were the most abundant in catches, hatchery-origin males weighed only 67% of wild males. The maximum observed age was 12 years for wild fish and 5 years for hatchery-origin fish. The instantaneous total mortality rates of hatchery-origin fish were more than twice as high as those of wild fish. In summary, the hatchery-origin fish had poor health status, poor growth and high mortality, and their fitness in natural environments was therefore hypothesized to be low throughout life.

Population dynamics of the Nile tilapia (Oreochromis niloticus L. 1758) stock in Lake Langeno, Ethiopia

Nile tilapia, Oreochromis niloticus, is a widely distributed and economically most import fish species in Ethiopia. Effective management is essential to sustain their fisheries and the benefits for the local communities. However, little is known about the population dynamics of the Nile tilapia stock in Lake Langeno. Vital parameters of its population were determined using length frequency data collected from 5,949 specimens ranging from 8.5 to 35.7 cm total length (tl). These specimens were collected from August 2017to July 2018. The population parameters were determined using the elefan I routine in FiSAT software. Estimated von Bertalanffy growth parameters were asymptotic length (L∞) = 35.70 cm, growth curvature (K) = 0.32 yr-1, age at length zero (to) = -0.49, and growth performance index (Փ') = 2.61. Instantaneous total mortality (Z), natural mortality (M), and fishing mortality (F) rates were determined from length-converted catch curve and empirical models, respectively, and their values obtained were Z = 2.31 yr-1, M = 0.82 and F =1.56 yr-1, respectively. The exploitation rate (E) of Nile tilapia computed from its mortality rates was 0.67 yr-1, suggesting state of overfishing. The size at first capture (Lc) was estimated at 14.0 cm which is much lower than the size at first maturity (Lm=16.62 cm), which further substantiated the state of overfishing. The results of the study are very useful for fishery managers and scientists who wish to manage and further explore the Nile tilapia stock in Lake Langeno.

Effects of age composition of Pacific bluefin tuna on their spatiotemporal distribution of active breeding in the south-western North Pacific and on its recruitment strength

Context The south-western North Pacific is one of the main spawning grounds of the Pacific bluefin tuna (Thunnus orientalis) and is targeted by Japanese longline fisheries. Aims This study evaluated the influence of age composition of spawning groups in this area on the strength of recruitment through the spatiotemporal distribution of active breeding. Methods The variation in the recent year-class strength in the area was estimated on the basis of the otolith age estimation and catch data from 2007 to 2016. Key results In the age–frequency distribution, 9 years was the most frequent age class. The instantaneous total mortality after 9 years of age was 0.32. Conclusions On the basis of catch locations and age estimation results, the bias toward young individuals influenced the spatiotemporal pattern of active breeding to shifts to higher latitudes and earlier breeding. In this area, the abundance of the main spawning group (9- and 10-year-old fish) may affect the recruitment of 0-year-old fish, and the older fish are considered to serve as a ‘seed bank’. Implications These results are expected to contribute to the development of appropriate management strategies for spawning stocks in the area and demonstrate the magnitude of the influence of age composition on population fluctuations.

Population dynamics of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) at Kelavarappalli Reservoir in Tamil Nadu

Nile tilapia, Oreochromis niloticus, is one of the most established among the introduced fishes in inland waters of India. The population characteristics of O. niloticus from Kelavarappalli Reservoir, a small reservoir of Tamil Nadu, were studied. The von Bertalanffy growth parameters (VBGF) were estimated using ELEFAN. The L∞values were 38.7 cm and 37.6 cm for males and females, respectively. The growth coefficient K was estimated at 0.65 (males) and 0.73 (females). The fishes showed isometric growth. The fishing mortality (F) was 2.4 yr-1, the natural mortality rate (M) was 1.2 yr-1 and the total instantaneous mortality rate (Z) was estimated at 3.6 yr-1. The probability of capture of O. niloticus was 25% at 12.2 cm, 50% at 12.7 cm and 75% at 16.9 cm size range. The relative yield-per-recruit (Y'/ R) and biomass-per-recruit (B'/ R) were derived from the growth parameters and the values were 0.33 and 1.88 respectively. The expected yield at various levels of fishing mortality shows that yield increased with increased fishing suggesting that it can be increased by enhancing the effort up to an exploitation rate (E) value of 0.56. The present exploitation rate (E= 0.67) is beyond MSY and therefore the catch is declining. To sustain the tilapia fishery at Kelavarapalli the exploitation rate should be brought down to 0.56 from the present 0.67. The biomass per recruit against exploitation ratio reveals that half the stock is reduced at an exploitation ratio of 0.31. Further expansion of fishing here will be detrimental to the stock of tilapia as it suffers from both growth overfishing and recruitment overfishing. Key words Growth; Instantaneous mortality; Exploitation rate; Relative yield per recruit

Preliminary observation on the sustainability of white sardine, Escualosa thoracata (Valenciennes, 1847), exploited from the central west coast of India

BackgroundThe present study assessed the growth and mortality parameters of the white sardine, Escualosa thoracata which is having high local demand. The white sardine gained importance due to its taste, and high demand in domestic markets as compared to the oil sardine necessitated a study on this resource to know the present status of exploitation level along the central west coast of India.ResultsA total of 3026 individuals of different size groups of E. thoracata were randomly collected from the Burondi fish landing center of the Ratnagiri district of Maharashtra. The asymptotic length (L∞) and growth coefficient (K) were estimated to be 115 mm and 1.9 year−1, respectively, by ELEFAN-I and 135 mm and 1.2 year−1 by the scattergram. The value of t0 by von Bertalanffy plot was estimated to be −0.000012 year. The fish attained a length of 65 mm, 94 mm, and 114 mm at the end of 0.5, 1, and 1.5 years of its life, respectively. The instantaneous rate of total mortality (Z), natural mortality (M), and fishing mortality (F) were estimated to be 8.07 year−1, 2.55 year−1, and 5.52 year−1, respectively. The exploitation rate (U) was calculated as 0.65, and the exploitation ratio (E) was 0.68.ConclusionThe growth, mortality, and other population parameters observed in the present study will help to understand the current stock status, which is pointing toward the over-fishing condition (E ˃ 0.50) of the white sardine in the study area. Therefore, the present investigation suggests reducing the fishing pressure on E. thoracata along the central west coast of India for the sustainability of the resource.

Age, Growth, and Mortality of Atlantic Tripletail in the North‐Central Gulf of Mexico

AbstractIn the southeastern USA and the Gulf of Mexico (GOM), Atlantic Tripletail Lobotes surinamensis are increasingly targeted by recreational anglers, indicating that stock status should be assessed. A critical need for such assessments is age‐specific data; however, previous studies have drawn conflicting conclusions regarding the most appropriate structure for aging. Moreover, growth parameters and mortality rates for GOM Atlantic Tripletail are unknown. Therefore, the goals of this study were to (1) evaluate sagittal otoliths and first dorsal spines as aging structures; (2) model combined and sex‐specific growth; and (3) estimate mortality rates for GOM Atlantic Tripletail. From 2012 to 2019, Atlantic Tripletail (N = 230, including a near‐record‐size specimen) were collected from the north‐central GOM via hook and line and were aged using otoliths and first dorsal spines. Total length ranged from 212 to 940 mm, and age ranged from 0.07 to 5.27 years. Otoliths produced higher percent agreement (95.0%) and lower average percent error (3.0%) between readers compared to spines (82.9% and 6.5%, respectively). The von Bertalanffy growth parameters differed slightly between the otolith‐based data (mean asymptotic length [L∞] = 762.42 mm, Brody growth rate coefficient [k] = 0.69 year−1, and hypothetical age at which length equals zero [t0] = −0.58 year) and spine‐based data (L∞ = 718.83 mm, k = 0.79 year−1, and t0 = −0.56 year). For both otolith‐ and spine‐based sex‐specific data, the best‐fitting version of the von Bertalanffy growth function permitted L∞ to vary by sex. Chapman–Robson estimates of instantaneous total mortality rate and total annual mortality rate were 1.15 and 68.66%, respectively. Based on empirical, life history‐based methods, the instantaneous natural mortality rate was estimated at 0.75–0.97 and the instantaneous fishing mortality rate was estimated at 0.18–0.45, suggesting low levels of exploitation. These growth parameters and mortality estimates will provide information for future stock assessments, thereby ensuring sustainability of the GOM stock of Atlantic Tripletail.

Population Structure of Pagellus Acarne (Risso, 1927) in the North Aegean Sea

Sparidae family is one of the most important demersal group for Turkish fisheries. When considering the importance of Turkey fisheries, population parameters of Pagellus acarne Risso, 1827 have a many proposition for future fisheries studies. Studies of biology and population parameters of this species are very limited in the Aegean Sea; therefore we aimed to determine population parameters (length-weight relationship, age and growth parameters, mortality rates and reproductive season) in order to obtain a data for the future studies. We caught 2673 Pagellus acarne specimens between September 2006 to September 2008 from monthly samples at depths ranging from 20 to 500 m in the Saros Bay using a commercial bottom trawl net. Total length and weight range from 3.5 to 27.1 cm, 1.93 to 314.5 g, mean length and weight were 14.0±0.05 cm, 35.6±0.46 g respectively. The length-weight relationship was detected W=0.001*L3.054, which indicated positive allometric growth. The high GSI value was in September. The data on maturity stages indicated that length at 50% maturity (L50) for females 18.1 cm TL for males 15.3 cm TL. The age data derived from sagitta otoliths reading were used to estimate the growth parameters and ranged from 1-4 aged. The von Bertalanffy growth parameters of the total were L∞=30.63 cm, K=0.26 year-1, to= -0.95. The instantaneous total mortality was Z= 0.72 year-1, the natural mortality M = 0.54 year -1, the fishing mortality F=0.19 year-1 respectively. The exploitation ratio (E) of the stock was found as 0.26. Pagellus acarne is the most important marine fish species with high commercial value for both Turkey coast and all the Mediterranean basin. This study aims to define basic population parameters which should be needed for further fisheries studies and management strategies in the in Saros Bay, the North Aegean Sea.

Individual growth and mortality of Rhithropanopeus harrisii (Decapoda: Panopeidae) in the estuarine region of Patos Lagoon, Southern Brazil

Abstract The present investigation aimed to estimate the individual growth and mortality of an invasive species found in the estuarine region of Patos Lagoon (Southern Brazil). For 20 months crabs were sampled, and in the laboratory specimens of Rhithropanopeus harrisii (Gould, 1841) were measured (carapace width, CW, and weight). Carapace width data was utilized for a modal progression analysis and to estimate the individual growth curve (von Bertalanffy growth model), and a size-converted catch curve. Von Bertalanffy parameters estimated were CW∞ = 16.92 mm and k = 1.28 year-1. Maximum longevity was estimated at 3.5 years. Instantaneous total mortality was estimated at 2.17 ± 0.30 year-1. It has been suggested that longevity may be explained by a low predation impact on R. harrisii, which, as a consequence, may lead to slow individual growth of this species in the estuarine region of Patos Lagoon.

Loggerhead marine turtle (Caretta caretta) ecological facts from a trophic relationship model in a hot spot fishery area: Gulf of Ulloa, Mexico

The oceanographic conditions in the Gulf of Ulloa (GU) region make a distinctive faunal assemblage, allowing the presence of species both ecologically and economically important. Constant interaction of emblematic species with the fishing activity has brought social and conservation problems due to the lack of ecological information and/or management tools. For the loggerhead turtle (Caretta caretta), the GU is an important feeding area, so the interaction with anglers is frequent. In this sense, some events of high loggerhead mortality have resulted in restrictive fishing measures; nevertheless, alternative hypotheses should be explored to explain this fact better. With the purpose of not only knowing the ecosystem ecological attributes but also obtaining specific ecological facts of the loggerhead turtle – as instantaneous total mortality – this study proposes Ecopath with Ecosim (EwE) model by calculating Allen's approximation of production to biomass ratio (P/B). Using the thermoregulation theory of ectotherms and this baseline model, the scenarios were run in Ecosim combining two forcing factors (FF): sea surface temperature (SST) and different fishing effort (F) values. All Ecosim scenarios were run over 30 simulated years taking the (P/B) values of the loggerhead turtle. According to the results in this study, the model allowed us to obtain specific ecological attributes for C. caretta, particularly for the P/B estimates in different simulation scenarios, which showed that colder sea surface temperature increases loggerhead mortality. All the information combined provided a better panorama to understand the role this turtle has within the Biological Action Center of the GU system and its interaction with other activities developed on site, such as fishing.

Using Acoustic Telemetry to Estimate Weakfish Survival Rates along the U.S. East Coast

AbstractThe Weakfish Cynoscion regalis, an economically important species, has declined over the last 30 years, corresponding with an increase in total mortality according to the most recent stock assessment. We estimated estuarine‐specific and coastwide apparent survival of Weakfish by using a Cormack–Jolly–Seber model to provide insights into the spatiotemporal component of mortality. Telemetered Weakfish (n = 342) were released across five estuaries ranging from North Carolina to New Jersey between 2006 and 2016. In estuaries from Delaware Bay and northward, egress peaked around the third week of September; in North Carolina, egress peaked by the first week of November. For three estuaries with adequate sample sizes, apparent survival estimates were similar and a joint model including all telemetered Weakfish estimated an extremely low annual apparent survival rate of 0.001 (95% credible interval [CrI] = 0.002–0.0003) or annual apparent instantaneous total mortality of 7.25 (95% CrI = 6.28–8.05). At a minimum, 61% of telemetered Weakfish emigrated in the fall, but only 2 of 149 fish with long‐lived transmitters were detected as returning to estuaries the following year. This is a small proportion for a fish that exhibits spawning site fidelity. We conclude that the disappearance of telemetered Weakfish represents mortality that occurs between emigration and the spring spawning period, potentially during overwinter periods on the continental shelf. Our study provides insights into the magnitude, timing, and location of Weakfish loss and facilitates an improved understanding of Weakfish population dynamics for use in stock rebuilding.

An integrated tagging and catch-curve model reveals high and seasonally-varying natural mortality for a fish population at low stock biomass

Rebuilding of exploited fish stocks at low biomass requires accurate mortality estimates. Weakfish (Cynoscion regalis) abundance is at historical lows caused by an increasing instantaneous total mortality (Z) in recent years, but uncertainty exists regarding the relative importance of instantaneous fishing mortality (F) and natural mortality (M) to Z. Data from a tag-return study and catch-curve of weakfish in North Carolina were analyzed jointly using a Bayesian statistical framework to estimate seasonal and annual mortality (i.e., F, M, and Z). We accounted for key auxiliary parameters in the tag-return portion of the model (i.e., tag-reporting rate and tag loss) through field studies and an experimental design, including use of high-reward tags and double tagging. Estimates of Z from the joint model were similar in magnitude to the weakfish stock assessment. From mid-2014 to 2017, we estimated a constant annual instantaneous mortality rate of 0.05 yr−1 (95 % credible interval [CrI]: 0.04, 0.07) for F and 2.33 yr−1 (CrI: 2.10, 2.6) for M. In the most recent stock assessment, estimates of M had an upper bound of 1.0; thus, our findings suggest that these estimates of M are biased low and F biased high. Our seasonal analyses showed that a large portion of mortality occurred from fall to spring, coinciding with weakfish migration and overwintering periods on the continental shelf. Through an integrated modeling approach, our study provides insights into the magnitude, timing, and sources of weakfish mortality, and enhances understanding of weakfish population dynamics to guide management strategies.