Fish Stock Assessment Research Articles

The Importance of Involving Stakeholders and Scientists in the Management of Marine Fisheries

In recent years there has been increasing concern over the state of fish stocks, especially those that support key fisheries and supply food to many consumers. There is also concern over the state of aquatic environments, and the effects of climate change. Fisheries management is controlled by government agencies, often cooperating with similar agencies from other nations. This paper deals with the need for expert advice on fisheries, involving fishers as well as scientists. Mention is made of a Fisheries Partnership set up in Europe, bringing fishers and scientists together with other stakeholders to discuss the problems of managing fish stocks. The partnership was especially successful in improving relationships between fishers and scientists, and made significant improvements to some fish stock assessments. European Regional Advisory Councils were later established to play a similar role. They are providing significant advice on fisheries, but they do not yet play a key role in actual management. It is important to consider how stakeholders and scientists can become more actively involved in fisheries management. There is a crucial need to develop new, more participatory ways of managing fisheries.

Including 38 kHz in the standardization protocol for hydroacoustic fish surveys in temperate lakes

AbstractHydroacoustics has become a requisite method to assess fish populations and allows to describe the relationships of fish with other elements of the aquatic ecosystem. This nonintrusive method is currently an integral part of the sampling procedures recommended for fish stock assessment by the Water Framework Directive and has been standardized by the European Committee for Standardization [CEN (2014) CSN EN 15910 ‐ Water quality ‐ Guidance on the estimation of fish abundance with mobile hydroacoustic methods, Category: 7577 Water quality. Biological.]. In Europe, hydroacoustic surveys are performed in freshwater using different frequencies. Consequently, there is a need to evaluate if survey results can be compared. This study aimed to carry out in situ comparisons at the 38 kHz frequency (noted f) with two other commonly used frequencies, 70 and 200 kHz. The 38 kHz frequency has seldom been compared with other frequencies in freshwater although it is widely used worldwide, especially in the Great Lakes of North America and in Sweden. In 2016, hydroacoustic data were acquired in Lakes Annecy and Bourget using methods validated in previous studies that compared the frequencies 70, 120 and 200 kHz. This study showed similar density and biomass estimations as a function of frequency, density(f) and biomass(f), between the frequencies studied for low to moderate fish densities. For higher fish densities, the results were more variable and need to be verified. Fish density(f) and biomass(f) estimations sometimes exhibit differences between frequencies, which is not fully in agreement with theoretical calculations. The aim of this study was to evaluate frequency comparisons in practise. However, if the differences on acoustic metrics, density(f) or biomass(f) between frequencies were occasionally statistically significant, the differences were small enough to be considered negligible for fish population management. These analyses led to better knowledge of the responses from fish in temperate lakes for the studied frequencies. Our findings should be considered when revising the CEN standard.

Unraveling the recruitment problem: A review of environmentally-informed forecasting and management strategy evaluation

Studies describing and hypothesizing the impact of climate change and environmental processes on vital rates of fish stocks are increasing in frequency, and concomitant with that is interest in incorporating these processes in fish stock assessments and forecasting models. Previous research suggests that including environmental drivers of fish recruitment in forecasting is of limited value, concluding that forecasting improvements are minimal while potential spurious relationships were sufficient to advise against inclusion. This review evaluates progress in implementing environmental factors in stock-recruitment projections and Management Strategy Evaluations (MSEs), from the year 2000 through 2017, by reviewing studies that incorporate environmental processes into recruitment forecasting, full-cycle MSEs, or simulations investigating harvest control rules. The only successes identified were for species with a short pre-recruit survival window (e.g., opportunistic life-history strategy), where the abbreviated life-span made it easier to identify one or a limited set of key drivers that directly impact dynamics. Autoregressive methods appeared to perform as well, if not better, for species with a longer pre-recruit survival window (e.g., seasonal, inter-annual) during which the environment could potentially exert influence. This review suggests that the inclusion of environmental drivers into assessments and forecasting is most likely to be successful for species with short pre-recruit survival windows (e.g., squid, sardine) and for those that have bottlenecks in their life history during which the environment can exert a well-defined pressure (e.g., anadromous fishes, those reliant on nursery areas). The effects of environment may be more complicated and variable for species with a longer pre-recruit survival window, reducing the ability to quantify environment-recruitment relationships. Species with more complex early life histories and longer pre-recruit survival windows would benefit from future research that focuses on relevant species-specific spatio-temporal scales to improve mechanistic understanding of abiotic-biotic interactions.

Evaluation of the effects of otolith sampling strategies and ageing error on estimation of the age composition and growth curve for Pacific bluefin tuna Thunnus orientalis

The age composition of the catch and the growth curve of a stock are fundamentally important in fish stock assessment, but these estimates are subject to various sources of uncertainty. Using the Pacific bluefin tuna (Thunnus orientalis) fisheries in the waters off Taiwan as an example, we developed a Monte Carlo simulation model to evaluate the effects of four otolith sampling methods (random otolith sampling, ROS; fixed otolith sampling, FOS; proportional otolith sampling, POS; and reweighting otolith sampling, REW), and ageing error (bias and imprecision) on estimations of age composition and growth curves. The results indicated that FOS has the lowest sampling accuracy, POS performs the best and that ROS is a more efficient method with lower estimation error. For an imprecise reader, the centre (median) of multiple age reads is a useful method to obtain accurate and precise estimates. Ageing bias had greater effects on the estimation of age composition and growth parameters than ageing imprecision or the selection of otolith sampling methods. In most cases, 500 otoliths should be an adequate sample size and could be the guideline for the biological sampling program of the T. orientalis Catch Documentation Scheme.

Importance of Considering Year-to-year Variability in Length-weight Relationship in a Size-based Fish Stock Assessment

Importance of Considering Year-to-year Variability in Length-weight Relationship in a Size-based Fish Stock Assessment

Indicators of stock status for large-pelagic fish based on length composition from driftnet fisheries in Zanzibar

Small-scale fisheries (SSF) contribute to approximately half of the total landings of tuna and tuna-like species in the Indian Ocean and are an important form of employment and source of protein. Research into the properties and dynamics of SSF in East Africa are important for the assessment and sustainable management of fish stocks, however, detailed fisheries data are often inadequate or absent. Fisheries-dependent data on driftnet fisheries in Zanzibar, Tanzania, was collected during the northeast monsoon seasons in 2014 and 2015. The data describes the properties of the driftnet fisheries and allows for comparisons of the length composition of the landings of the SSF with large-scale industrial fisheries (IF) fishing in Tanzania’s Exclusive Economic Zone (EEZ). This data also facil - itates the calculation of stock indicators for the five most abundant tuna and tuna-like species landed in Zanzibar. Results show that the two fisheries (SSF and IF) exploit the same stocks, and landings are representative of a similar length composition, while operating in different parts of Tanzania’s EEZ. High exploitation rates, above reference levels for all species were calculated, in agreement with official assessments by the IOTC, and suggest that calls for the expansion of the SSF should be reconsidered. The assessment and management of straddling stocks are dis - cussed, as well as solutions to challenges faced by local observer programmes.

Snorkeling‐Based Fish Stock Assessment by Anglers—A Valuable Method for Managing Recreational Fisheries

AbstractPeriodic assessment of harvested fish populations is essential for their sustainable management. A potential alternative to costly and resource‐intensive electrofishing estimates in clearwater streams is the noninvasive snorkeling method. To assess the utility of snorkeling for the angling community, we compared underwater fish counts carried out by novice snorkelers to state‐of‐the‐art electrofishing depletion estimates. Over two consecutive years, we sampled subadult and adult Brown Trout Salmo trutta and Rainbow Trout Oncorhynchus mykiss with both methods in a fourth‐order mountain stream. In each year, a new team of novice snorkelers collected the data. In total, 12 riffle, pool, and run habitats were sampled, and the homogeneity of abundance and size‐class distribution between the two methods was analyzed. Over both years, we could detect differences in 6 of 24 habitat × species configurations and in 10 of 72 habitat × species × size‐class configurations. Species‐specific behavioral traits and differences in the physical character of the habitats were responsible for a divergence in performance between the two methods. Overall, the observed effects were statistically interpreted as weak, as shown by local tests and the indicated low effect sizes. Snorkeling efficiency, however, remained affected by the effort and abilities of the team, as indicated by the year‐by‐year comparison. We conclude that in clearwater trout streams, snorkeling can be an appropriate substitute method for the widespread, autonomously organized angling community to gather data and build a sound foundation for fisheries‐related decision making, if limitations are considered.

Length-weight relationships of three popular fishes from Banda Aceh, Indonesia

Study on the length-weight relationships and conditions factors of three popular fishes consumption has been done in Banda Aceh in October 2017. This study was conducted to stock assessment and condition of fish. The data was collected at Lampulo Fishery Port, Banda Aceh. Data analysis was done using linear allometric Model (LAM). The results of the length-weight relationships showed that all three species of fish experienced negative allometric growth patterns. The highest b value is shown in Sardinella fimbriata with a value of 2.44, followed by Oreochromis niloticus (2.30) and Euthynnus affinis (2.08). The value of Fulton’s (K) condition factor indicates that all three fish species have value> 1.6 with a mean of 3.03. Furthermore, the value of relative weight (Wr) condition factor of three types of fish shows a value> 100 with a mean of 100.23. Thus it can be concluded that the values of K and Wr indicate the environmental conditions of the three types of fish in a stable condition.

A modelling approach to evaluate the impact of fish spatial behavioural types on fisheries stock assessment

Abstract Spatial behavioural types (SBTs) arise from between-individual differences in behavioural traits that foster spatial behavioural patterns that are consistent over time and ecological contexts. Fish stocks are regularly assessed using catch per unit effort (CPUE) as input data that may non-linearly co-vary with the underlying abundance (N) of the exploited stock when SBT affect catchability. We hypothesized that SBT promote characteristic changes in catchability within harvesting seasons that affect catch rates and in turn catch-based fish stock assessments. To test this hypothesis, we developed a spatially explicit agent-based simulation where we measured encounters between fish and fishers and estimated the shape of the CPUE–N relationship. We ran the simulation in a prototypical fish–fisher encounter-leads-to-catch-type fishery and systematically studied outcomes in the presence or absence of SBTs. It was revealed that the existence of SBTs leads to CPUE inevitably declining faster than N (a process known as hyperdepletion) when compared with a simulation lacking SBTs. This finding was consistent in a wide range of fishing effort scenarios. The emergent hyperdepletion of catch rates was caused by fast and behavioural-selective exploitation of vulnerable SBT that encompassed the mobile component of the fish stock. The theoretical predictions received support from field data from a coastal recreational fishery. Our work suggests that the consideration of SBT when interpreting trends in CPUE data may notably improve stock assessments by providing a more reliable CPUE–N relationship.

Length-weight relationship and stock assessment of tuna fish (<i>Euthynnus affinis</i>) in East Halmahera waters

The study was conducted in December 2016 to February 2017 in East Halmahera waters with the aim to examine the relationship between the length of weight and potential and the level of utilization of tuna. The results showed that the long frequency distribution of tuna was ranging from 10.0-28.2 cm, with a maximum length value of 29.93 cm, a growth coefficient of 0.74 per month and a measure of fish worth catching for spawning. The relationship between the weight of tuna in East Halmahera waters is W=0.0078L3.2982, where the length of tuna is greater than this weight increase due to environmental conditions and oceanographic parameters that affect the growth of tuna. The results of the MSY analysis or the sustainable resource potential of tuna in East Halmahera waters using the Fox method, found that the MSY value or sustainable potential of tuna was 4,176.54, with a maximum effort level of 8,047 Trips. This utilization rate is still low from the value of MSY and continues to decline this is due to the low value of fishing efforts.

Using Three Acoustic Technologies on Underwater Gliders to Survey Fish

AbstractAutonomous platforms and vehicles are a growing component of the ocean research fleet, producing data sets crucial to our understanding of oceanographic and fishery ecosystem processes. One emerging tool for making these measurements is underwater gliders that autonomously sample the water column for weeks to months at a time. Although originally designed to measure temperature and salinity, underwater gliders can now support a myriad of sensors. For the demonstration project described within, three complementary acoustic technologies were integrated into an underwater glider for mapping fish on the continental shelf: an acoustic telemetry receiver, a passive acoustic monitoring recorder, and a fisheries echosounder.The demonstration project was designed to evaluate the effectiveness of each sensing technology. Sixty-one fish were implanted with acoustic tags near the Gulfstream Natural Gas pipeline in the eastern Gulf of Mexico in advance of planned underwater glider missions. The glider was deployed four times over 12 months, with all three acoustic technologies to traverse the pipeline and surrounding habitat. Glider detections were compared to detections of fish at moored acoustic tag telemetry receivers and passive acoustic recorders co-located at the tagged fish locations. All three technologies identified fish along the targeted hard-bottom pipeline habitat, as well as previously uncharted areas of hard-bottom reef. The results of this study demonstrate the utility of gliders integrated with acoustic sensors as a potential tool to identify areas that merit deeper investigation to assess fish stocks.

Inclusion of ecosystem information in US fish stock assessments suggests progress toward ecosystem-based fisheries management

Abstract The appetite for ecosystem-based fisheries management (EBFM) approaches has grown, but the perception persists that implementation is slow. Here, we synthesize progress toward implementing EBFM in the United States through one potential avenue: expanding fish stock assessments to include ecosystem considerations and interactions between species, fleets, and sectors. We reviewed over 200 stock assessments and assessed how the stock assessment reports included information about system influences on the assessed stock. Our goals were to quantify whether and how assessments incorporated broader system-level considerations, and to explore factors that might contribute to the use of system-level information. Interactions among fishing fleets (technical interactions) were more commonly included than biophysical interactions (species, habitat, climate). Interactions within the physical environment (habitat, climate) were included twice as often as interactions among species (predation). Many assessment reports included ecological interactions only as background or qualitative considerations, rather than incorporating them in the assessment model. Our analyses suggested that ecosystem characteristics are more likely to be included when the species was overfished (stock status), the assessment is conducted at a science centre with a longstanding stomach contents analysis program, and/or the species life history characteristics suggest it is likely to be influenced by the physical environment, habitat, or predation mortality (short-lived species, sessile benthic species, or low trophic-level species). Regional differences in stomach contents analysis programs may limit the inclusion of predation mortality in stock assessments, and more guidance is needed on best practices for the prioritization of when and how biophysical information should be considered. However, our results demonstrate that significant progress has been made to use best available science and data to expand single-species stock assessments, particularly when a broad definition of EBFM is applied.

FISH CATCH QUOTA ASSESSMENT FOR SUSTAINABLE MARINE FISHERIES RESOURCES IN EAST JAVA

Fish resources Information urgently needed by development planners in fisheries sectors,especially for fisheries development. The fisheries resources utilization in East Java tends to be overexploited.This caused uncertainty of fishing activities for the traditional fishermen in the East Java waters. Some studies ofpopulation dynamics and fish stock assessment described fisheries resources exploitation in some areas of EastJava was on fully exploited to overexploited condition. The aim of this research were; [1] to know sustainablepotential and total allowable catch of fisheries resources in the area of Pasuruan regency, Probolinggo Regency,and Banyuwangi regency; [2] tho know the utilization status of fisheries resources in the area of Pasuruanregency, Probolinggo Regency, and Banyuwangi regency; and [3] to determine the empowerment strategy forfishermen community in order to utilize fisheries resources in the area of Pasuruan regency, ProbolinggoRegency, and Banyuwangi regency. The analyses were done through the calculation of sustainability potential,and total allowable catch, and determine the controlling strategy of fisheries resources utilization. The studydescribed that the comparison analysis of fishing trip data, fish catch and total allowable catch in the sustainablecondition was in the overexploited condition. Moreover, based on the analysis of fisheries resources utilizationstatus in the research area, the controlling strategy was created based on the recommendation of all stakeholders.This strategy including the management of the fishing area, management of fishing time, and determine ifalternative activities in the scope of both fisheries and non-fisheries sectors. These strategies can be used as abasic data in determining an empowerment strategy for fishermen in the fisheries resources utilization. Thesestrategies including accompaniment approach and information services through community and ecosystem-basedof fisheries resources management.

БИОЛОГИЧЕСКОЕ РАЗНООБРАЗИЕ НА БЕНИНСКОМ КОНТИНЕНТАЛЬНОМ ШЕЛЬФЕ ВО ВРЕМЯ ИССЛЕДОВАНИЯ ОЦЕНКИ ЗАПАСОВ ДЕМЕРСАЛЬНЫХ РЫБ

The global objectives of this study are to assess biodiversity composition in the tested trawling areas during the survey period. This study cannot take in account all species that can occur in the fishing areas because of the shortness of the work. To have a most complete list of species it will be better to carry out the survey covering four hydrologic periods (2 hot and 2 cold hydrologic periods) to have a chance to meet most of the species. However, the work was done during the most important period for the study. This study was conducted in terms of the demersal fish stock assessment survey initiated by the West African Economic and Monetary Union in the continental shelves of states members and neighboring countries (Côte d'Ivoire, Ghana, Togo and Benin) for the south part of Africa in order to determine fish population and abundance. In the waters of Benin, there have been listed 100 fish species including 76 demersal species (69 bony and 7 cartilaginous fish) and 13 pelagic species consisting entirely of bony specimens. Species richness, according to the reports of trawling stations, varies between 28 and 7 species. Fish abundance is the largest at the depth of 25-50 m. According to the data of station 10, species number makes 7.76% of the total, followed by station 19 with 26 taxa at the depth of 50-100 m. The lowest taxon number is registered in station 4 at a depth of 10-25 m with 4 taxa representing 1.94% of all targeted. The Simpson's index is close to 0, varying between 0 and 0.049, it shows a great diversity especially in the first stratum of 10 to 25 m. This study allows to evaluate species diversity in different fishing areas and consequences of the significant increase of fishing pressure on the stand and not only to focus on a few populations of species of commercial interest.

Comments on incongruous formulations in the SAM (state-space assessment model) model and consequences for fish stock assessment

The stock assessment model SAM (state-space assessment model) is an important tool for analysing fishery data and is used for abundance estimation of several different fish stocks. We demonstrate incongruous formulations in the equations that relate the catch data to fish abundance, and in the fishery and natural mortality rates. We present example results to show how these formulations introduce bias, and compound the uncertainty in model estimates. Finally, we provide corrections to the system equations to remedy the drawback.

Empirical acoustic TS - Length relationship for Torpedo Scad (Megalaspis cordyla)

One of the main challenge in fish stock assessment with acoustic method is how to improve the accuracy of the estimated acoustic target strength (TS) of the fish under investigation. Various factors contribute to the bias in acoustic TS, namely the high diversity of fish species, body shape, orientation and size. It is therefore necessary to have a database of acoustics TS of fish on a particular species, size (length), and orientation as a reference to be used in grouping and in estimating the over all TS-length relationship of the species. In this paper we reported the result of in situ TS measurements of Torpedo Scad (Megalaspiscordyla). The TS data analysis is performed numerically through the best-fit technique to establish the relationship between length, object orientation, and TS. The TS-length relationship obtained for Torpedo Scad (Megalaspis cordyla) is TS = 20 log (FL)–53.68.This relationship could be used to eliminate bias in the fish stock assessment by acoustic method.

BÀN VỀ ĐIỀU TRA NGHỀ CÁ THƯƠNG PHẨM Ở BIỂN VIỆT NAM

In fish stock assessment, two approaches have been used to collect data: Fisheries independent survey and fisheries survey. Fisheries independent survey provides scientific information on species composition, catch rate, density, distribution, standing stock biomass and biological information of certain species while fisheries survey supplies primary data for a wide variety of statistical analysis of fisheries performance. In Vietnam, fisheries survey was first developed by project “Assessment of the Living Marine Resources in Vietnam” with the support of DANIA since 1998 as the pilot study in 11 coastal provinces with the purpose of establishing the fisheries statistical system in Vietnam. After the pilot stage, it has been extended to all of 28 coastal provinces and worked effectively since 2000. In 2006, when the project ended, the fisheries statistical system collapsed due to no finance support to continue. Since July 2014, the fisheries data collection network has been recovered with the collaboration of Directorate of Fisheries, Research Institute for Marine Fisheries and Provincial Departments of Capture Fisheries and Marine Resources Protection. The survey design was the logbook base with applying the sampling in space and in time method. This is an overview of the capture fisheries survey in Vietnam with its limitations and challenges.

Inland fish stock assessment: Applying data‐poor methods from marine systems

AbstractInland fisheries can be diverse, local and highly seasonal. This complexity creates challenges for monitoring, and consequently, many inland fish stocks have few data and cannot be assessed using methods typically applied to industrial marine fisheries. In such situations, there may be a role for methods recently developed for assessment of data‐poor fish stocks. Herein, three established data‐poor assessment tools from marine systems are demonstrated to highlight their value to inland fisheries management. A case study application uses archived length, catch and catch‐per‐unit‐effort data to characterise the ecological status of an important recreational brown trout stock in an Irish lake. This case study is of specific use to management of freshwater sport fisheries, but the broader purpose of the paper was to provide a crossover between marine and inland fisheries science, and to highlight accessible data‐poor assessment approaches that may be applicable in diverse inland systems.

The population dynamics of a recently introduced crayfish, Cherax quadricarinatus (von Martens, 1868), in the Sanyati Basin of Lake Kariba, Zimbabwe

The redclaw crayfish Cherax quadricarinatus is a recent introduction into Lake Kariba, Zimbabwe where it is rapidly spreading. There are, however, no studies that have investigated the population dynamics and possible ecological impacts of the crayfish in the lake. This study investigated aspects of the population biology of C. quadricarinatus in the lake. These included sex distribution, population growth and mortality parameters, probability of capture, recruitment and length at age of ge at maturity. Crayfish were captured monthly between January and December 2013 from 13 sites using opera house bait traps. Aspects of the species population biology were estimated using a fish stock assessment tool, FISAT II. A total of 3 205 crayfish were captured, of which 44% were male, 49% female and 7% intersex individuals. The asymptotic length (L∞ = 112.88 mm), curvature parameter (k = 0.72), longevity (tmax = 4.17 years), growth performance index (ϕ = 3.96), total mortality (Z = 2.06 y−1), fishing mortality (F = 1.07 y−1), natural mortality (M = 0.99 y−1), rate of exploitation (E = 0.52) and length-at-first capture (Lc = 44.48 mm) were estimated. Fecundity averaged 503 ± 229 eggs female−1 and increased with size (weight and carapace length). Gravid females were found throughout the year but the highest proportion of females with eggs (4–10%) were found in the first quarter, whereas recruitment peaked in May and June. The smallest crayfish with eggs (48.75 mm CL) was estimated to be 1.02 years and the largest (94.82 mm CL) 2.85 years. Cherax quadricarinatus exhibited an r strategy life-history pattern due to continuous reproduction and high fecundity. In Lake Kariba, C. quadricarinatus is now well into the establishment stage of the Introduction–naturalisation–invasion continuum and spreading in the lake. Management options should thus aim at preventing further spread and reducing the population size and the potential negative impacts of this species.

Combined use of trawl fishery and research vessel survey data in a multivariate autoregressive state-space (MARSS) model to improve the accuracy of abundance index estimates

Fishery-dependent catch per unit effort (CPUE) data have been used as an abundance index (AI) in fish stock assessments. However, fishery-dependent CPUE data are influenced not only by changes in fish abundance but also by other factors, such as the choice or restrictions of fishing grounds to operate. Accordingly, bias may arise in AIs due to a lack of data from unfished or rarely fished areas. To improve the accuracy of AI estimates, spatially arranged CPUE datasets from both trawl fisheries and research vessel surveys in the East China Sea were concurrently analyzed in the present study using a multivariate autoregressive state-space (MARSS) model. Survey datasets complemented information on stock status in the fishing areas where fishery-dependent datasets were limited. As a result, the combined use of datasets from both sources effectively improved the accuracy of estimates of AIs and the spatial distribution of the population density of each fish species.