Assessment of the risk of commercial fisheries to New Zealand seabirds, 2006–07 to 2012–13

Citation

Richard, Y., & Abraham, E. R. (2015). Assessment of the risk of commercial fisheries to New Zealand seabirds, 2006–07 to 2012–13. New Zealand Aquatic Environment and Biodiversity Report No. 162. 89 p. Retrieved from https://www.mpi.govt.nz/document-vault/10523

Summary

This report, together with the supplementary information, presents an assessment of the risk of fisheries-related mortalities to 70 species and sub-species of seabirds that are breeding in New Zealand. The risk assessment considered all fishing by commercial trawl, bottom-longline, surface-longline and set-net methods within the outer boundary of New Zealand’s Exclusive Economic Zone. It built on a previous seabird risk assessment that was carried out in 2013, and a subsequent workshop held by the Ministry for Primary Industries that involved a range of seabird specialists. The workshop was aimed at identifying the limitations of the risk assessment and at updating relevant data, with the outcomes including recommendations for species demographic data, at-sea seabird distributions, and species and fisheries groupings used in the assessment.

This update of the previous seabird risk assessment followed the recommendations, and included two additional years of data, the 2011–12 and 2012–13 fishing years. Risk was defined as the ratio of annual potential fatalities (an estimate of the number of birds killed in fisheries each year) to the Potential Biological Removal (PBR; a measure of the reproductive capacity of the populations). The estimation of the PBR included a calibration factor, rho, to adjust the calculation of the maximum growth rate and total population size, and to ensure that the population goals are met in the presence of environmental stochasticity. The appropriate value for rho (ranging between between 0.17 and 0.61) depends on the species type. In addition, the PBR generally includes a recovery factor f that protects against errors in the demographic estimates used to calculate it. Here, the recovery factor f was set to 1, guided by the "National Plan of Action – 2013 to reduce the incidental catch of seabirds in New Zealand fisheries" (NPOA). The PBR with the calibration factor, and with a recovery factor of one, is referred to as PBRrho. The estimation of annual potential fatalities was based on data of seabird captures recorded by government fisheries observers and of fishing effort in trawl, bottom- and surface-longline, and set-net fisheries. A risk ratio larger than one indicates that the fishing-related fatalities in commercial fisheries exceed PBRrho, and the population will be at risk of not being able to remain above half its carrying capacity.

In total, there were 16 200 (95% c.i.: 12 600–21 000) estimated annual potential seabird fatalities across the four fishing methods in the seven-year period from 2006–07 to 2012–13. The highest number of annual potential fatalities were in trawl fisheries with 11 500 (95% c.i.: 8040–16 300) estimated annual potential fatalities. In comparison, there were a total of 2920 (95% c.i.: 2300–3700) annual potential fatalities in bottom-longline fisheries. Seabird fatalities in surface-longline fisheries were lower, with a total of 1420 (95% c.i.: 1150–1740) annual potential fatalities of all seabirds. There were fewer estimated fatalities in set-net fisheries, with a total of 294 (95% c.i.: 203–414) annual potential fatalities of all species. These estimates of annual potential fatalities depended on assumptions that were made about the extent of cryptic mortalities (birds that are killed by the fishing activity but not brought on-board the fishing vessel or included in captures reported by fisheries observers).

Following the risk categories in the NPOA, seven species were considered to be at "Very high risk", including black petrel, Salvin's albatross, southern Buller's albatross, flesh-footed shearwater, Gibson's albatross, New Zealand white-capped albatross, and northern Buller's albatross. The risk ratio of black petrel was especially large, with a median of 11.34 (95% c.i.: 6.85–19.81), due to the combination of a high number of estimated annual potential fatalities (mean 1130; 95% c.i.: 840–1490), and a low PBRrho (mean 100; 95% c.i.: 60–147).

Four species were considered to be at "High risk", including Chatham Island albatross, Antipodean albatross, Westland petrel, and Campbell black-browed albatross. Eight species were at "Medium risk", and another ten species were at "Low risk". Among the 70 considered species, 41 species had "Negligible risk" suggesting that commercial fisheries in New Zealand waters are unlikely to significantly impact the populations of these species.

Changes in the risk ranking from the previous assessment (which was corrected for some errors in the implementation) were primarily due to updated demographic data and to changes in the way seabird species and fisheries were grouped for estimating the annual potential fatalities. Chatham Island albatross was previously considered to be at "Very High" risk, but was found to be at "High risk" in the current assessment. This decrease was due to assessing small-vessel bottom-longline fishing targeting ling separately to other small-vessel fisheries that targeted this species. Gibson's albatross was at "High" risk in the previous assessment, but was found to be at "Very High" risk here. This increase in the risk ranking was due to assessing wandering and royal albatrosses separately. Other changes included Campbell black-browed albatross moving into the "High risk" category, northern royal albatross moving from "High risk" to "Medium risk", Stewart Island shag moving from "Low risk" to "Medium risk", and Snares Cape petrel moving from "High risk" to "Low risk". These changes were due to updates in the demographic parameters, changing the definition of Cape petrel to exclude Antarctic Cape petrel, and changing the grouping of the seabird species.

This seabird risk assessment allowed an assessment of the impacts of a wide range of commercial fishing on New Zealand seabirds. Risk was quantified, placing the estimated annual potential fatalities in a population context. The relative stability in the assessment, given the changes that were made since the previous assessment, indicated that the methodology is maturing. Over time, it will allow for fisheries related changes in the risk to be assessed. Possible improvements include a better specification of cryptic mortality. Poor knowledge of cryptic mortality restricts understanding of the impacts of fisheries on seabird populations. Other improvements include increased observer coverage in small-vessel fisheries that currently have limited observer data. As the risk assessment requires adequate observer data, increasing observer coverage in these fisheries would reduce the uncertainty associated with the current estimates of risk. The assessment could also be extended to include broader impacts, such as seabird captures in recreational fisheries, and in global fisheries.

Supplementary information is available in a separate document.