Indicators of body size variability in a highly developed small-scale fishery: Ecological and management implications

Abstract

Body size plays a key role for the productivity and resilience of marine populations. This work analyses the variation in body size indicators taken from ~ 400 000 individuals during the period 2000–2018 for a set of 20 key commercial species of the small-scale fishery of Galicia (SW Europe). Mean body size showed relatively stable inter-annual trends during the study period, and, at the year level, mean body size for most species followed seasonal cycles. Body size was negatively related to the number of individuals caught per haul. Bathymetry also explained part of the variation in individual body size with species-specific depth affinities. Common trends in the species’ body size showed an increasing trend in the northern region while decreasing in the south suggesting differences in local environmental conditions and/or in the dynamics of the fishery. The skewness of body size distributions varied slightly from year to year, although some species showed significant trends. The annual trend of the species-specific skewness was negatively related to the proportion of immature individuals in the catch and positively related to the rate of change in abundance, suggesting a reduction of recruitment success in response to differences in size-selective exploitation patterns probably ascribed to minimum landing size being generally below size at maturity. The combination of body size and abundance indicators revealed a relatively stable performance of some of the most important resources targeted by the Galician small-scale fishery sector during the last two decades. However, our study highlights also the need to align management measures with biological reference points in order to prevent long-term reductions in stock productivity.

Keywords

• Body size
• Skewness
• Length at maturity
• Linear mixed effects models
• Dynamic factor analysis
• Small-scale fishery