Standardization of bluefin tuna, Thunnus thynnus, catch per unit effort in the baitboat fishery of the Bay of Biscay (Eastern Atlantic)

Abstract

Relative indices of abundance by age class for bluefin tuna from 1975 to 2000 were estimated using generalized linear mixed models. Age class was included as a fixed factor within the model specifications, with the Year×Age interaction as a fixed factor component in order to obtain annual indices by age. Catch and effort data on bluefin tuna were available from two sources, catches by trip, and daily catches from logbooks. Catches were modelled using the delta-lognormal model. The model finally selected included the following explanatory factors: Year, Age, Year×Age, Month, number of Crew, number of Bait Tanks, and with the Year×Month interaction as a random component. Overall, year trends and coefficients of variation were similar from both datasets by age class. In general, the standardization procedure showed that vessel characteristics and technological advances related to fishing have a relatively minor explanatory effect on the observed catch rates of bluefin tuna in the fishery. Neither geographical distribution nor type of bait had an explanatory effect on the observed catch rates. The 1994 cohort stands out as an exceptionally large year class; it can be followed through the standardized series. This standardized catch rate index at age of bluefin tuna is the most complete yet available and is the only one currently used for juvenile fish in calibrating population models to evaluate the Eastern Atlantic and Mediterranean stock. It is particularly valuable because, apart from improvements in electronic technology, there are no changes in the method of exploitation during the entire series.

Standardizing catch and effort data: a review of recent approaches

“…Bigelow et al (1999) used a GAM approach to model the catch rate of swordfish (Xiphias gladius) and blue shark (Prionace glauca) in the North Pacific, and found highly-nonlinear relationships between, for example, latitude and longitude and catch rate. Rodríguez-Marín et al (2003) used a GAM approach to determine whether the catch rates of bluefin tuna (Thunnus thynnus) in the Bay of Biscay varied with longitude and latitude.…”

“…Several recent analyses of catch and effort data (e.g. Chang, 2003;Miyabe and Takeuchi, 2003;Rodríguez-Marín et al, 2003;Brandão et al, 2004;Ortiz and Arocha, 2004) treated some of the parameters as random effects. In general, random effects have been introduced into models to deal with interactions between year and other categorical variables, such as area (see Section 5 for further details).…”

“…A binary random variable is zero for a zero observation and unity otherwise, and has, by definition, a Bernoulli distribution with probability parameter, w. The probability of obtaining a zero observation is therefore usually modeled using the binomial distribution (e.g. Vignaux, 1994;Stefánsson, 1996;Punt et al, 2000a;Rodríguez-Marín et al, 2003). A variety of distributions could be used to model the catch rate given that it is non-zero.…”

Molecular expression of opsin gene in growing juvenile mackerel (Scomber japonicus Houttuyn)

“…This species plays an important role in live bait for the fishery of tuna in Spain (Rodriguez et al 2003). Due to higher economic value based on protein source for human consumption and typical food products for the aquaculture industry, a considerable number of studies have been carried out in mackerel over past decades (Park et al 1973;Cha et al 2004;Yoon et al 2008).…”

Looking for skin and gill parasites as biological tags for Atlantic bluefin tuna (Thunnus thynnus)

“…21, 365-371 (2008) patterns and distribution associated with fish size and presumed natal origin (Rooker et al 2007). The Bay of Biscay is a summer feeding area for ABFT juveniles, where they are found from June to October in the southeast corner of the Bay, [43][44][45][46][47] • N, 2-6 • W, near the coast (Rodríguez-Marín et al 2003). Conventional tagging data indicate a significant exchange of juveniles between the Bay of Biscay, the IberoMoroccan Bay and the western Mediterranean Sea, and even some transatlantic migrations between the Bay of Biscay and the western Atlantic (Cort 1990;Mather et al 1995;Rooker et al 2007).…”