Global patterns of sex- and age-specific variation in seabird bycatch [SBWG8 paper]

Understanding sex- and age-biases in seabird bycatch rates is important for assessing population-level impacts. We provided the first global assessment of seabird bycatch by sex and age, investigating the effects of region and fishing method. Bycatch was highly biased by sex (65% of 123 samples) and age (92% of 114 samples), with the majority of samples skewed toward males and adults. Bycatch of adults and males was higher in subpolar regions, whereas there was a tendency for more immatures and females to be killed in subtropical waters. Fishing method influenced sex- and age-ratios only in subpolar regions. Sex- and age-biases are therefore common features of seabird bycatch in global fisheries that appear to be associated largely with differences in at-sea distributions. This unbalanced mortality influences the extent to which populations are impacted by fisheries, which is a key consideration for at-risk species.
RECOMMENDATIONS
1. Tracking individuals of different sex and age classes to improve knowledge of their relative overlap with vessels, and hence susceptibility to bycatch.
2. Collecting data on sex, age and provenance of bycaught birds by fisheries observers in order to identify regions and fleets where bycatch is more likely to result in population-level impacts, and to improve targeting of bycatch mitigation and monitoring of compliance.
3. Including sex-specific effects when investigating the influence of fisheries on life history traits of albatrosses and petrels to improve our understanding on the impact of fisheries on their population dynamics.