Importance of Shallow Tidal Habitats as Refugia from Trawl Fishing for Sea Snakes
Sea snakes are an important component of bycatch in commercial and small-scale trawl fisheries in tropical waters and are highly vulnerable to fishing-related mortality. Extensive boat-based surveys were conducted to investigate the assemblage and abundance of sea snakes within a protected shallow coastal bay adjacent to productive trawl fishing grounds. Spine-Bellied Sea Snakes, Hydrophis curtus (previously Lapemis curtus), and Elegant Sea Snakes, Hydrophis elegans, were the most commonly encountered species. Based on the age structure of these two species, the bay was used primarily by juveniles. Temporal trends in age structure and sex ratios showed that H. curtus may use Cleveland Bay as a nursery ground, with gravid females entering the bay in summer months to give birth. In contrast, H. elegans appears to use the bay more consistently through the year, with ∼30% of individuals being adults. This study also showed that shallow tidal habitats, too shallow for trawl fishing, are regularly used by sea snakes and may provide refugia for vulnerable life stages. The identification and protection of such habitats may further mitigate risks to sea snake populations from trawl fishing.Abstract
Map of Cleveland Bay, Australia. Boat-based surveys were conducted between October 2012 and October 2014 in the area within black dashed line. Broken grey lines indicate bathymetry within the bay.
Survey effort (130 trips) within Cleveland Bay throughout the 2-yr period where trips averaged 4.13 h of search time. The number of trips in each 3-mo period is represented within each bar.
Size frequency of Hydrophis curtus (white bars) and Hydrophis elegans (grey bars) captured in Cleveland Bay. Vertical broken lines indicate limits between the adult and juvenile age classes based on size at sexual maturity from Ward (2001).
Age structures of (A) Hydrophis curtus and (B) Hydrophis elegans caught within Cleveland Bay (grey bars) compared to age structures of the same species caught in trawl fisheries from previously published data (white bars; Ward, 2001).
Temporal trend in the proportion of juvenile, male, nonreproductive female, and gravid female (A) Hydrophis curtus and (B) Hydrophis elegans caught in Cleveland Bay. Number of adults and juveniles caught are represented in parentheses above and below plots, respectively.
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