Assessment of the risk of commercial fisheries to New Zealand seabirds, 2006–07 to 2016–17

Seabirds are incidentally caught in commercial fisheries in New Zealand waters, with a range of species featuring in bycatch records across different fisheries. The potential impact of these incidental captures on seabird populations breeding within New Zealand’s Exclusive Economic Zone has been regularly assessed through a systematic risk assessment framework, which allowed the identification of species and fisheries associated with the highest risk and the monitoring of changes in risk status over time. The risk assessments are based on the Spatially Explicit Fisheries Risk Assessment (SEFRA) framework, which allows risk to be calculated for all species and fisheries of interest, even when bycatch and population data are incomplete or uncertain. The present analysis provides an updated assessment of the risk of commercial fisheries in New Zealand for 71 seabird taxa breeding in the New Zealand region, including data to the 2016–17 fishing year.

The SEFRA risk assessment framework is based on an estimation of the rate at which seabirds encounter fishing effort, based on spatial overlap between seabird and fishing effort distributions, and the probability of incidental capture or death per encounter. The estimation is based on data from government observers, who record incidental captures onboard commercial fishing vessels. These bycatch records are extrapolated to the unobserved fishing effort, based on the spatial overlap, while taking into account cryptic mortality (deaths that are not observable). The resulting total fishery-related deaths (D) are then compared to a Population Sustainability Threshold (PST), which is the maximum number of fisheries deaths that the population can sustain while still achieving a defined population objective. The calculation of this Population Sustainability Threshold (PST) for each species is based on demographic information, such as population size and productivity. The ratio of total fishery-related deaths to the PST is referred to as the “risk ratio”, which can be specific to a particular fishery or cumulative across fisheries to yield total fisheries risk at the species level.

The default population outcome (ϕ) applied in the current update of the multi-species seabird risk assessment was ϕ = 0.5, to ensure that populations for which the risk score is less than 1 will recover to or stabilise at a level at or above 75% of the non-impacted status. Species-specific risk assessments may define other population outcomes, reflecting different policy goals for particular species.

The current update of the previous seabird risk assessment included two additional years of data, from 2015–16 and 2016–17. In addition, discrepancies identified during the preparation of fishing effort and observer data for the 2016–17 fishing year were corrected, including data discrepancies in earlier fishing years. The update was carried out in three stages, distinguishing differences through the addition of more recent data from differences caused by the data correction. No changes were made to the demographic parameters that inform the risk assessment nor to the modelling approach used to estimate the number of captures.

When updating the previous risk assessment with the corrected data, there was only one change in risk category at the species level: for spotted shag, it increased from “low risk” to “medium risk”, suggesting that the corrections only had a minor impact on the results. Compared with the previous assessment for the period from 2012–13 to 2014–15, estimating risk for the 2014–15 and 2016–17 fishing years following the corrections, led to a change in risk category for four species: the risk ranking decreased from “high risk” to “medium risk” for Chatham Island and New Zealand white-capped albatrosses, and from “medium risk” to “low risk” for spotted shag. In contrast, there was an increase in the risk category for white-chinned petrel, with a change from “negligible risk” to “low risk”.

Black petrel remained at “very high risk” from commercial fisheries; it was the only species at the highest risk ranking. There were five taxa in the second-highest category, with Salvin’s albatross, Westland petrel, flesh-footed shearwater, southern Buller’s albatross and Gibson’s albatross assessed to be at “high risk” from fisheries. While the species-level risk score for black petrel was relatively unchanged from previous risk assessments, the current assessment estimated that the greatest fisheries risk to black petrel is from inshore trawl fisheries; previously, bottom-longline fisheries were estimated to pose the greatest risk to this species.

The findings from the risk assessments support New Zealand government’s framework for reducing the impact of fishing on New Zealand seabird populations, outlined in the draft “National Plan of Action - Seabirds 2020” to reduce the incidental catch of seabirds in New Zealand fisheries.