scholarly journals ON STOCK ASSESSMENT AND FORECASTING THE STOCK ABUNDANCE OF NORTH SHRIMP PANDALUS EOUS MAKAROV, 1935 NEAR SOUTH-WESTERN KAMCHATKA

2019 ◽  
pp. 72-91
Author(s):  
Oleg I. Ilyin ◽  
◽  
Oхana G. Mikhaylova ◽  
Keyword(s):  
Stock Assessment ◽  
Western Kamchatka ◽  
Stock Abundance

Interaction Between Stock Area, Stock Abundance, and Catchability Coefficient

1985 ◽  
Vol 42 (5) ◽  
pp. 989-998 ◽  
Author(s):  
G. H. Winters ◽  
J. P. Wheeler
Keyword(s):  
Stock Assessment ◽  
Population Decline ◽  
Clupea Harengus ◽  
Atlantic Herring ◽  
Population Abundance ◽  
Commercial Catch ◽  
Standard Manner ◽  
Clupea Harengus Harengus ◽  
The Relationship ◽  
Stock Abundance

The relationship between commercial catch-rates and population density upon which many stock assessment models depend assumes that stock area (A) is constant and independent of population abundance. Starting from a theoretical demonstration that the catchability coefficient (q) is inversely proportional to A, we establish the empirical basis of this relationship through comparisons of q and A of various Northwest Atlantic herring (Clupea harengus harengus) stocks and, in more detail, for Fortune Bay herring. For these stocks the relationship was of the form q = cA−b. For Atlantic herring stocks, levels of b were in excess of 0.80. In Fortune Bay herring, reductions in abundance were accompanied by proportional reductions in A, which in turn was inversely correlated with changes in q. School size, measured as catch per set, also declined as population levels declined but the change was not proportional. Published findings indicate that pelagic stocks in particular, and fish stocks in general, exhibit a common response of reductions in A with interactive increases in the q during periods of rapid population decline. We conclude that the conventional assumption of a constant stock area is usually violated due to the systematic interaction between A and population abundance which is reflected in an inverse relationship between stock abundance and q. Calibration of sequential population models should therefore be restricted to research vessel data collected in a standard manner and covering the distributional area of the stock.

The Galápagos sea cucumber fishery: management improves as stocks decline

2004 ◽  
Vol 31 (2) ◽  
pp. 102-110 ◽  
Author(s):  
S.A. SHEPHERD ◽  
P. MARTINEZ ◽  
M.V. TORAL-GRANDA ◽  
G.J. EDGAR
Keyword(s):  
Sea Cucumber ◽  
Fishery Management ◽  
Stock Assessment ◽  
Research Capacity ◽  
Rapid Expansion ◽  
Management Framework ◽  
Galapagos Archipelago ◽  
Management Controls ◽  
Marine Wildlife ◽  
Stock Abundance

The Galápagos Islands, a world heritage region for the protection of the unique terrestrial and marine wildlife, are also home to a small human population, dependent on fisheries. There was a lucrative sea-cucumber (Stichopus fuscus) fishery in the islands, which began in 1992. After a rapid expansion in the Galápagos archipelago, the fishery has declined and now persists predominantly around the western islands. Initially, the fishery was largely illegal and uncontrollable. Subsequently, a co-management framework developed, with fisher participation. Gradually enforcement improved, apparent corruption declined, and research capacity increased. Although stock abundance surveys have been carried out annually since 1993, the paucity of background biological and fishery information does not allow rigorous stock assessment. The achievements of co-management through the participation of fishers in research and management have been: an acceptance of management controls on numbers of fishers and quotas, a reduction in conflict and increased co-operation. Persistent problems have been: weak enforcement capacity, limited funds for patrolling and research, corruption and declining stock abundance. Proposed application of precautionary principles to management, including a range of fishery indicators, may save the fishery from collapse. The principles are applicable to many other data-poor fisheries globally.

Reconciling conflicting survey indices of abundance prior to stock assessment

2021 ◽  
Author(s):  
Cassidy D Peterson ◽  
Dean L Courtney ◽  
Enric Cortés ◽  
Robert J Latour
Keyword(s):  
Relative Abundance ◽  
Assessment Tool ◽  
Stock Assessment ◽  
Assessment Model ◽  
Dynamic Factor ◽  
Shark Species ◽  
Southeast United States ◽  
Structured Population ◽  
Age Structured ◽  
Stock Abundance

Abstract Indices of relative abundance are one of the most important inputs into a stock assessment model. For many species, we must rely on several indices that routinely conflict with each other and which may result in biased and uncertain outputs. Here, we explored whether reconciled trends obtained from dynamic factor analysis (DFA) applied to conflicting indices can be used as a trend of relative abundance input into a stock assessment model. We simulated an age-structured population of two coastal shark species in the southeast United States to generate multiple disagreeing indices, reconciled the indices using DFA, and then inserted both the multiple conflicting survey indices and the simplified DFA-predicted trend into respective stock assessment models. We compared the results of each stock assessment model to simulated values to evaluate the relative performance of each approach. We found that the DFA-based assessment generally performed similarly to the conflicting index-based assessment and may be a useful assessment tool in situations where conflicting indices with different selectivities, catchabilities, variances, and missing data are present. DFA assessment results were more consistent across simulation scenarios and outperformed many conflicting index assessments when surveys underwent shifts in catchability and the underlying stock abundance exhibited contrast.

scholarly journals Characterization and standardization of the Atlantic albacore French pelagic trawl fishery

2018 ◽  
Vol 31 ◽  
pp. 27
Author(s):  
Natacha Nikolic ◽  
Matthew Lauretta ◽  
Audrey Patucca ◽  
Gilles Morandeau
Keyword(s):  
North Atlantic ◽  
Stock Assessment ◽  
Sea Surface ◽  
Seasonal Effects ◽  
Trawl Fishery ◽  
Generalized Linear Modelling ◽  
Linear Modelling ◽  
Logbook Data ◽  
Stock Abundance

We compiled and analysed logbook data from the French trawl albacore fishery covering the period 1991–2015. The dataset comprised catch and effort data for the French fleet operating in the Bay of Biscay and Celtic Sea, as well as spatiotemporal and gear characteristics. Generalized linear modelling was used to model spatial, seasonal, environmental, and gear covariates of fleet CPUE rates. A long-term index of relative abundance is provided that can be integrated into the stock assessment of North Atlantic albacore. The analysis revealed higher albacore CPUE associated with relatively low sea surface temperature and distinct seasonal effects. The derived abundance trend for the French trawl fishery agreed with the estimated time series of stock abundance from recent assessments.

Fleet dynamics of herring trawlers—change in gear size and implications for interpretation of catch per unit effort

2002 ◽  
Vol 59 (3) ◽  
pp. 531-541 ◽  
Author(s):  
Mika Rahikainen ◽  
Sakari Kuikka
Keyword(s):  
Stock Assessment ◽  
Fish Stock ◽  
Catch Per Unit Effort ◽  
Unit Effort ◽  
Fish Stock Assessment ◽  
Fleet Dynamics ◽  
Changes Over Time ◽  
Index Of Abundance ◽  
Over Time ◽  
Stock Abundance

Catch per unit effort (CPUE) is widely used as an index of stock abundance. It is as widely acknowledged that CPUE can be a misleading index of abundance owing to a multitude of factors including fish behavior, fishing fleet interaction, and the increase in catchability over time caused by improvement in fishing technology. Based on information concerning the size of herring trawls manufactured in Finland since the early 1980s, an increase in fishing power of the fleet was postulated. Because we lacked direct information about the size of trawls aboard, we applied a model to estimate the changes over time. In the analysis, an analogy between fish and trawls was created by adopting the concepts and algorithms from fish stock assessment into assessment of the trawl "population", where both the total number of trawls and the size of individual trawls were being analyzed. The results indicate that the average gear size has nearly tripled in 20 years. Accepting the assumption that larger trawls are generally more effective than smaller ones, a substantial increase in fishing power has taken place. As a result, sequential population models calibrated with CPUE data will be severely biased as well.

Studies on southern Australian abalone (Genus Haliotis), 16. Recruitment, habitat and stock relations

1995 ◽  
Vol 46 (3) ◽  
pp. 669 ◽  
Author(s):  
SA Shepherd ◽  
D Partington
Keyword(s):  
Habitat Complexity ◽  
Water Movement ◽  
Stock Assessment ◽  
South Australia ◽  
Total Mortality ◽  
Fertilization Success ◽  
Recruitment Failure ◽  
Stock Recruitment ◽  
Size At Sexual Maturity ◽  
Stock Abundance

The dynamics of a population of the greenlip abalone, Haliotis laevigata, was studied from 1978 to 1990 in Waterloo Bay, South Australia. During this period the fishery was closed from 1982 to 1986 and the size limit was increased in 1986. The spatial distribution of recruitment (measured as the abundance of the 2+ age class) was correlated during every year of study with a complex gradient comprising water movement, habitat complexity and predator density, and for six years of the study with depth. Recruitment in the six years from the closure was 2.7 times higher than that in the preceding seven years. stock assessment, fecundity, total mortality, size at sexual maturity, sex ratio. The intensity of aggregation of the adult (≥4 years) fraction of the population varied with density and habitat complexity. Under intense fishing, aggregations were fewer and smaller. This paper weights stock abundance according to a model relating intensity of aggregation with fertilization success and presents a stock-recruitment relation for the Waterloo Bay population. The curve is a classical Ricker type showing compensation at high stock sizes. This curve indicates that below adult densities of about 0.15 to 0.2 m-2 the population is increasingly vulnerable to recruitment failure and ultimately to collapse.

scholarly journals Uncertainty in stock assessment estimates for New England groundfish and its impact on achieving target harvest rates

2018 ◽  
Vol 75 (3) ◽  
pp. 342-356 ◽  
Author(s):  
John Wiedenmann ◽  
Olaf P. Jensen
Keyword(s):  
New England ◽  
Stock Assessment ◽  
Scientific Uncertainty ◽  
Multiple Sources ◽  
Potential Yield ◽  
Historical Levels ◽  
Stock Abundance

Overfishing continues for many stocks in the New England groundfish complex despite efforts to constrain harvest rates and rebuild populations. We evaluated the magnitude and sources of scientific uncertainty in catch targets for groundfish and found that since 2004, annual harvest rates have been 151% above the target while catches have been 29% below the target catch, on average, resulting from overly optimistic catch targets for the majority of stocks. Multiple sources of scientific uncertainty contributed to this overestimation, but the largest contributor was overestimated abundance. By evaluating sequential assessment estimates, we found previous assessments frequently overestimated terminal abundance. Additional uncertainty in catch targets resulted from recent recruitments often being below historical levels. The net effect of overly optimistic catch targets and declining recruitment is that rebuilding has been sluggish and potential yield (and revenue) has been forgone for many stocks. The causes of the overestimation of stock abundance and declines in recruitment remain unknown, but because these patterns were widespread, there may be common mechanisms in the region influencing assessment estimates and stock productivity.

FIRST RECORD AND INITIAL HYDROACOUSTIC STOCK ASSESSMENT OF POLLAN COREGONUS AUTUMNALIS PALLAS IN LOUGH ALLEN, IRELAND

2010 ◽  
Vol 110 (1) ◽  
pp. 69-74 ◽  
Author(s):  
Andrew J. Harrison ◽  
Fiona L. Kelly ◽  
Robert S. Rosell ◽  
Trevor W.S. Champ ◽  
Lynda Connor ◽  
...  
Keyword(s):  
Stock Assessment ◽  
First Record
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