Systematics, fishery and biology of the white sardine Escualosa thoracata (Valenciennes, 1847) exploited off Kerala, south-west coast of India
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Landings of the white sardine Escualosa thoracata (Valenciennes, 1847) indicated a shift in their abundance from northeast to south-west coast of India and a sharp decline in the resource landings during the last decade along the entire range of its distribution. High local demand coupled with competitive price for the species might have led to overexploitation of this otherwise seasonal resources along the major areas of its abundance along the Indian coast. Detailed study on the systematics, fishery and biology of the species landed along Kerala coast was undertaken during 2015 and 2016. Stock assessment studies indicated near optimum fishing pressure on the resource along the Kerala coast.Keywords:
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Abstract Demer, D. A., Zwolinski, J. P., Cutter, G. R. Jr, Byers, K. A., Macewicz, B. J., and Hill, K. T. Sampling selectivity in acoustic-trawl surveys of Pacific sardine (Sardinops sagax) biomass and length distribution. – ICES Journal of Marine Science, 70: . To annually assess the northern stock of Pacific sardine (Sardinops sagax) in the California Current and set harvest quotas for the US fishery, managers have used an age-structured stock synthesis model fitted with results from acoustic-trawl (ATM), daily-egg-production, and aerial-photogrammetric survey methods, fishery landing and individual-length data, and many assumed or empirically derived parameters. In these assessments, sardine landed at ports spanning from Ensenada, México to Vancouver Island, Canada were assumed to be solely from the northern stock. It was also assumed that the ATM estimates of sardine biomass were negligibly biased for the sizes of fish sampled by the survey trawls (i.e., catchability q = 1 for sardine standard length (SL) values greater than ∼17 cm). Due to these catchability and length-selectivity assumptions, the ATM- and assessment-estimated abundances are mostly similar for larger sardine. However, the assessment estimates include large abundances of small sardine (SL values less than ∼15 cm) that are not represented in either the ATM-survey results or the fishery landings, and generally did not recruit to the migrating northern stock sampled by the ATM surveys. We considered four explanations for this disparity: (i) the ATM length-selectivity assumption is correct; (ii) the non-recruiting small fish may comprise a smaller portion of the stock than indicated by the assessments; (iii) during years of low recruitment success, those size classes may be virtually completely fished by the Ensenada and San Pedro fisheries; or (iv) they may belong to the southern sardine stock. This investigation emphasizes the previously identified importance of differentiating samples from the northern and southern stocks and surveying their entire domains.
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We used CANSAR (Catch-at-age ANalysis for SARdine, an age-structured stock-assessment model) and a wide range of data to estimate bioniass and recruitnient of Pacific sardine (Savdinops sagax) off California and northern Baja California during 1983-95. Daily egg production method (DEPM) spawning bioniass estimates and an abundance index from CalCOFI data based on generalized additive niodels were iniportant new sources of information. Biomass (344,000 MT of sardine age 1+ during July 1995, CV = 33%) increased by 28% year-’. Fishing mortality (particularly for older ages) after 1991 was high and probably not sustainable under average environmental conditions. DEPM data for sardine during 1986-88 and 1994 niay have underestimated spawning bioniass due to incomplete coverage of spawning habitat. There was a modest potential for bias in the DEPM data due to nonrepresentative sampling of young age groups by survey gear. On the basis of experience with DEPM data for sardine and northern anchovy (Engraulis rnovdax), we make suggestions about how DEPM data should be used for fish stock assessment and fishery management. Size-at-age declined during 1983-95 and was significantly correlated with sardine biomass.
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We estimate the biomass of the Pacific sardine (Sardinops saga) population (age one and older) off California and northern Baja California on July 1, 1996 to have been about 5 10,000 short tons (CV 44% and 95% confidence interval from 287,000 to 1,099,000 tons ). Our estimate was based on output from a stock assessment model called CANSAR. For the first time, biomass estimates from CANSAR were compared to biomass estimates from two other stock assessment models (Virtual Population Analysis or VPA and an age structured model without catch at age data). Results from all three models were similar, although there was considerable uncertainty in biomass estimates for recent years. Questions about stock structure and distribution were major sources of uncertainty in our sardine assessment. Recent data show increased sardine abundance in the Pacific Northwest off the Columbia River and as far north as British Columbia, but we were unable to determine if those fish were part of the stock available to the California fishery and whether the biomass of sardine in northern areas was included in estimates from OUT models. Similar questions exist about sardine in Mexican waters south of Ensenada. These problems were confounded by the fact that our survey and fishery data which were mostly collected within the Southern California Bight. We suggest that additional information is needed to resolve these questions because different modeling approaches gave similar results.
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The primary goal of sardine management as directed by the California Fish and Game Code is rehabilitation of the resource with an added objective of maximizing sustained harvest. Accordingly, the Code states that the annual sardine quota can be set at an amount greater than
1,000 tons, providing that the level of take allows for continued increase in the spawning population.
We estimated the sardine population size to have been 464,000 short tons on July 1, 1997. Our estimate was based on output from a modified version of the integrated stock assessment model called CANSAR (Deriso et al. 1996). CANSAR is a forward-casting, age-structured analysis using fishery-dependent and fishery-independent data to obtain annual estimates of sardine abundance, year-class strength and age-specific fishing mortality for 1983 through the
first semester of 1997. Non-linear least-squares criteria are used to find the best fit between model estimates and input data.
Questions about stock structure and range extent remain major sources of uncertainty in assessing current sardine population biomass. Recent survey results and anecdotal evidence suggest increased sardine abundance in the Pacific Northwest and areas offshore from central and
southern California. It is difficult to determine if those fish were part of the stock available to the California fishery. In an attempt to address this problem, the original CANSAR model was reconfigured into a Two-Area Migration Model (CANSAR-TAM) which accounted for sardine
lost to the areas of the fishery and abundance surveys due to population expansion and net emigration. While the model includes guesses and major assumptions about net emigration and recruitment, it provides an estimate which is likely closer to biological reality than past
assessments. The original CANSAR model was also used and estimates are provided for comparison.
Based on the 1997 estimate of total biomass and the harvest formula used last year, we recommend a 1998 sardine harvest quota of 48,000 tons for the California fishery. The 1998 quota is a decrease of 11% from the final 1997 sardine harvest quota for California of 54,000
tons. (55pp.)
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During the last century, the population of Pacific sardine
(Sardinops sagax) in the California Current Ecosystem has exhibited large fluctuations in abundance and migration behavior. From approximately 1900 to 1940, the abundance
of sardine reached 3.6 million metric tons and the “northern stock” migrated from offshore of California
in the spring to the coastal areas near Oregon, Washington, and Vancouver Island in the summer. In the 1940s, the sardine stock collapsed and the few remaining sardine schools concentrated in the coastal region off southern California, year-round, for the next 50 years. The stock gradually recovered in the late 1980s and resumed its seasonal migration between regions off southern California and Canada. Recently, a model was developed which predicts
the potential habitat for the northern stock of Pacific sardine and its seasonal dynamics. The habitat predictions were successfully validated using data from sardine surveys
using the daily egg production method; scientific trawl surveys off the Columbia River mouth; and commercial sardine landings off Oregon, Washington, and Vancouver Island. Here, the predictions of the potential habitat and seasonal migration of the northern stock of sardine are
validated using data from “acoustic–trawl” surveys of the entire west coast of the United States during the spring
and summer of 2008. The estimates of sardine biomass and lengths from the two surveys are not significantly
different between spring and summer, indicating that they are representative of the entire stock. The results
also confirm that the model of potential sardine habitat can be used to optimally apply survey effort and thus minimize random and systematic sampling error in the biomass
estimates. Furthermore, the acoustic–trawl survey data are useful to estimate concurrently the distributions and abundances of other pelagic fishes.
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The daily egg production method (DEPM) has been used to estimate the spawning biomass of Pacific sardine (Sardinops sagax) since 1986. In this paper, we document the current DEPM procedure using as an example the 2004 survey which incorporates the new procedures adopted since 1997. An adaptive allocation survey design used for sardine eggs has been successfully implemented. Yet, other issues associated with estimating spawning biomass of Pacific sardines remain. We also examine the time series of DEPM spawning biomass estimates and associated parameters from 1994 to 2004 and compare them to the spawning stock biomass (SSB) estimates derived from stock assessment models. The spawning biomass estimates off California increased from less than 10,000 mt in 1986 to 118,000 mt in 1994, to nearly 300,000 mt in 2004 and have fluctuated during the recent years. The spatial distribution of Pacific sardine eggs varied with sea surface temperature. The average fish weight doubled in the last 10 years, as has the reproductive rate.
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Abstract Two stocks of Pacific Sardine Sardinops sagax migrate seasonally and synchronously along the west coasts of Mexico, the USA, and Canada. Landings from the two stocks are currently combined in U.S. assessments of the northern stock, but the stocks may be differentiated by their associated seawater habitats, which are predominantly characterized by different ranges of sea surface temperature. We compared the combined and temperature‐differentiated landings of the two stocks in each country for the period 1993–2011, demonstrating how different attributions of the landings affected the estimated annual fishing fraction ( F ) for the northern stock. Using combined or stock‐differentiated landings and assessed biomasses, we found that the current harvest control rule (HCR) for Pacific Sardine has not consistently maintained a total F below the U.S. target value because the “distribution” parameter (used to account for the northern stock's proportion in the U.S. Exclusive Economic Zone [EEZ]), has not adequately accounted for northern stock landings in Mexico and Canada. We propose a refinement to the HCR, giving explicit consideration to the summed landings in Mexico and Canada, to more optimally set the annual U.S. quota. The performance of our method was compared with (1) the values of F that would have been achieved during the federal management period (2000–2011) if the U.S. quotas had always been met and (2) the generally lower actual values of F that were calculated using the default HCR formulation (1993–2011). We demonstrate that application of our method would permit more U.S. fishing for Pacific Sardine when the northern stock is large and predominantly located in the U.S. EEZ and would curtail U.S. fishing when a large proportion of the stock is present and fished in the Mexican EEZ, Canadian EEZ, or both. Received December 12, 2013; accepted July 16, 2014
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