Jan Horbowy, Magdalena Podolska and Krzysztof Radtke
Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland
Key words: cod, groundfish survey, GLM, Baltic Sea.
Abstract.
Polish groundfish survey data were analyzed using generalized linear models
(GLM) to investigate fish distribution, year-class strength and stock size.
Negative binomial errors were assumed for the analysis of young fish numbers
(age 1 and 2), while gamma error distribution was applied for the analysis of
adult fish biomass. The abundance of young fish was significantly dependent
on year of birth, depth, area (longitude, latitude), quarter and gear used in
the survey. The highest numbers were caught in the area demarcated by 15�50'E-
16�10'E while the lowest catches were made in the area demarcated by 17�00'E-17�30'E.
The maximal abundance was observed in the 50-70 m depth range. Cod at age 2
were more susceptible to survey gear catches than age group 1. The year-class
strength indices correlate relatively well with recruitment estimates from analytical
models (R2 = 0.6). The survey biomass of adult cod was significantly
dependent on year, depth, longitude and gear. The highest biomass concentration
was in an area demarcated by 15�50'E-16�50'E at a depth of 70-100 m. The indices
determined for adult stock size correlate relatively well with the spawning
stock biomass from analytical models (R2 = 0.57).