2 research outputs found
Working group on cephalopod fisheries and life history (Wgceph; outputs from 2022 meeting)
Rapports Scientifiques du CIEM. Volume 5, nÂş 1WGCEPH worked on six Terms of Reference. These involved reporting on the status of stocks;
reviewing advances in stock identification, assessment for fisheries management and for the Ma-
rine Strategy Framework Directive (MSFD), including some exploratory stock assessments; re-
viewing impacts of human activities on cephalopods; developing identification guides and rec-
ommendations for fishery data collection; describing the value chain and evaluating market driv-
ers; and reviewing advances in research on environmental tolerance of cephalopods.
ToR A is supported by an annual data call for fishery and survey data. During 2019–2021, com-
pared to 1990–2020, cuttlefish remained the most important cephalopod group in terms of weight
landed along the European North Atlantic coast, while loliginid squid overtook octopus as the
second most important group. Short-finned squid remained the least important group in land-
ings although their relative importance was almost double in 2019–2022 compared to 1992–2020.
Total cephalopod landings have been fairly stable since 1992.
Cuttlefish landings are towards the low end of the recent range, part of a general downward
trend since 2004. Loliginid squid landings in 2019 were close to the maximum seen during the
last 20 years but totals for 2020 and 2021 were lower. Annual ommastrephid squid landings are
more variable than those of the other two groups and close to the maximum seen during 1992–
2021. Octopod landings have generally declined since 2002 but the amount landed in 2021 was
higher than in the previous four years.
Under ToR B we illustrate that the combination of genetic analysis and statolith shape analysis
is a promising method to provide some stock structure information for L. forbsii. With the sum-
mary of cephalopod assessments, we could illustrate that many cephalopod species could al-
ready be included into the MSFD. We further provide material from two reviews in preparation,
covering stock assessment methods and challenges faced for cephalopod fisheries management.
Finally, we summarise trends in abundance indices, noting evidence of recent declines in cuttle-
fish and some octopuses of the genus Eledone.
Under ToR C, we describe progress on the reviews of (i) anthropogenic impacts on cephalopods
and (ii) life history and ecology. In relation to life history, new information on Eledone cirrhosa
from Portugal is included.
Under ToR D we provide an update on identification guides, discuss best practice in fishery data
collection in relation to maturity determination and sampling intensity for fishery monitoring.
Among others, we recommend i) to include the sampling of cephalopods in any fishery that (a)
targets cephalopods, (b) targets both cephalopods and demersal fishes or (c) takes cephalopods
as an important bycatch, ii) Size-distribution sampling, iii) the use of standardized sampling pro-
tocols, iv) an increased sampling effort in cephalopod.
Work under ToR E on value chains and market drivers, in conjunction with the Cephs & Chefs
INTERREG project, has resulted in two papers being submitted. Abstracts of these are in the
report.
Finally, progress under ToR F on environmental tolerance limits of cephalopods and climate en-
velope models is discussed, noting the need to continue this work during the next cycle.info:eu-repo/semantics/publishedVersio
Fisheries stock assessments for commercial Alaskan species, accounting for age-size-structured population dynamics
Thesis (Master's)--University of Washington, 2017-06This thesis develops a framework for conducting stock assessments that unifies age- and size-structured assessment models, creating what we term “age-size-structured models.” Several studies have explored the application of age-size-structured models to fisheries data. However, most are specific applications or were limited in scope. There is a dearth of generalized single-stock age-size-structured assessment models, which led to the creation and testing of such a model. An age-size-structured assessment method is developed, and examined first using a simulation study, and then using data for two species in the Eastern Bering Sea: Tanner crab (Chionoecetes bairdi) and Pacific cod (Gadus macrocephalus). Simulations are used to test under which conditions the assessment method is biased or imprecise. The simulations are summarized using a measure of the relative error between true and estimated spawning stock biomass. The simulation study suggested little bias and relatively high precision, such that the estimation method was considered acceptable for use in management. The results from the example application were compared to those from the official NOAA assessments. The estimates of mature male biomass for Tanner crab were found to be similar to those from the most recent stock assessment, but the estimates of spawning stock biomass for Pacific cod differed between the age-size-structured model and the latest official assessment, particularly after the mid-2000s. Some of the dissimilarity may be because maturity and growth are modelled based on size-dynamics in the age-size-structured model, while the official assessment considers only age-dynamics. Nevertheless, the age-size-structured model produces relatively robust estimates, and could be used as an alternative model to which current stock assessments could be compared. This generalized age-size-structured fishery stock assessment method could be applied to any data-rich stock globally, particularly where a species exhibits a mix of age- and size-based life history and fishery dynamics