Life history traits and abundance of Northeast Atlantic fish

Life history characteristics such as asymptotic length L∞, growth rate K, the length at which 50% of the individuals have reached maturity Lmat, and natural mortality M are therefore often used to indicate the sensitivity of different species to fishing. When species-specific information is missing, an estimate of the maximum length Lmax of a species can be used to infer asymptotic length, growth rate, natural mortality, and proportion mature at length. Here, we provide a data base containing life history parameters of 271 species along with the references of these values and gear efficiency estimates for all species. Further, we provide average annual catch indices within inhabitated areas for each species. 

Methods
Species recorded in the DATRAS survey database covering the Northeast Atlantic from the coast of Portugal to the North Sea and from the Baltic Sea to west of Scotland (http://www.ices.dk/data/data-portals/Pages/DATRAS.aspx) are included in the data. The maximum length of the species, Lmax, the asymptotic length, L∞, the von Bertalanffy growth rate parameter, K, length at first maturity, Lmat, and the length at which the individuals entered the sensitivity model (length at birth for chondrichthyan and length at metamorphosis for bony fish), Lmin, were derived from a comprehensive literature review.

Bottom and beam trawls retain a variable proportion of the fish found in the path of the gear. Some species, such as shallow water or reef-associated species, are difficult to catch because their habitat is not consistently sampled during trawl surveys, while pelagic species, such as Atlantic herring Clupea harengus are found in the water column and may pass above the headline of the gear without being caught. Furthermore, among the individuals that enter the mouth of the gear, the smaller individuals and species may escape through the meshes. Towed gears will therefore generate species and size specific fishing mortalities in the area where they operate. Walker et al. (2017) estimated the relative efficiency by which different species groups and sizes of fish were retained by the major towed commercial fishing gears operating in the North Sea. Dividing the species according to their body shape and typical vertical position in the water column, catch efficiency at length (exploitation pattern) was calculated for seven groups. We allocated the species to these groups:

Species group

Group description

1

Predominately buried in sediment

2

On or near the seabed – eel-like

3

Predominantly on the seabed – flat

4

Predominantly close to the seabed, but not on it

5

Midwater species with some seabed association

6

Pelagic

7

Predominantly on seabed – lumpiform

Catch indices were estimated as average catch per 30 min haul in the area in which the species had been recorded at least once using DATRAS data. Further details can be found in the paper. Average catch indices are only given for the most sensitive species.