Review of available information on non-key shark species including mobulids and fisheries interactions
This analysis collates all the observed information for non-key sharks (NKS) in the Western and Central Pacific Ocean (WCPO) purse seine and longline fisheries. NKS include all elasmobranchs not listed key sharks by the Western and Central Pacific Fisheries Commission (WCPFC). In order to assess the detail of observer reporting over time, from 1994 to 2015, trends in reporting rates were assessed for purse seine and longline fisheries separately. We present the data for purse seine data separately for fish aggregating device (FAD) sets (associated) and free school sets (unassociated sets). For the longline fishery the data were seperated into albacore target (those sets where albacore comprised 50% or more of the tuna catch) and bigeye-yellowfin tuna sets (those sets where bigeye and yellowfin tuna combiled comprised more than 50% of the tuna catch).
The data showed that for both longline and purse seine key sharks make up about 85-90% of the elasmobranch catch. Observers on longline vessels are better at, or the logistics of the operation enable better species reporting of NKS. On longline vessels most (over 80%) NKS are recorded at the species level; for purse seine observed sets, species specific reporting became more prevalent in 2007 and has fluctuated between 50-60% of individuals being identified to species level. This may be a result of grab spill sampling. Some obvious species specific trends exist where reporting rates of, for example, pelagic stingray Pteroplatytrygon violacea have increased in recent years.
Observed catch distribution maps are presented for both purse seine and longline gear separately and nominal CPUE trends are also presented. The fate of fish and condition at capture and release of the top 20 species or species complexes are presented.
For Manta birostris, Mobula sp. and P. violacea distribution plots are presented grouped into five year periods from 1995-2015 for purse seine and longline fisheries each separated by fleet type. In addition more detailed CPUE indices are presented for each gear type and set type.
Finally we review the available information on M. birostris; Mobula sp.; and P. violacea for consideration of these species for designation as WCPFC key sharks. As part of that assessment we suggest that the management of M. birostris and P. violacea could be enhanced if they were designated as key sharks by the WCPFC. However, improving observers abilities to identify individual Mobula sp. to a species level is likely to lead to improved information in the medium-term but listing them as a key shark species will probably not enhance the management of individual species at this stage.
The following recommendations are made:
Recommendation: Purse seine observer training programmes add emphasis to Mobula sp. identification as part of their curricula.
General recommendations for enhancing the key shark designation table:
•In future key shark species designation assessments tables include ”Is the management of likely to be enhanced by having it listed as a WCPFC key shark species?”.
•In future key shark species designation assessments include ”SCxx recommends that WCPFCyy list/does not list as a key shark species”.