First assessment of orange roughy stocks in the South Indian Ocean indicates their abundance is healthy condition
The Scientific Committee’s first stock assessment, of orange roughy was undertaken at its 3rd meeting. Patrick Cordue, who has a long history of undertaking stock assessments of this species for the New Zealand government was contracted to undertake this work. Cordue is a specialist in the use of NIWA’s stock assessment package CASAL. This advanced software package is becoming the international standard in the assessment and management of fish stocks, including some of the world’s most prized species. A NIWA-developed advanced software package is becoming the international standard in the assessment and management of fish stocks, including some of the world’s most prized species.
CASAL (C++ Algorithmic Stock Assessment Laboratory CASAL) is an advanced software package that uses a generalised age- or length-structured fish stock assessment model that allows choice in specifying the population dynamics, parameter estimation, and model outputs. It is flexible and can implement an age- or size-structured model or structure the population by sex, maturity, and/or growth-path. It can analyse a single stock for a single fishery, or for multiple stocks, areas, and/or fishing methods. The data used can be from many different sources, e.g. catch-at-age or catch-at-size data from commercial fishing, survey and other biomass indices and survey catch-at-age or catch-at-size data. Estimation can be by either maximum likelihood or a Bayes Estimate. As well as generating point estimates of the parameters of interest, CASAL can calculate likelihood or posterior profiles and can generate Bayesian posterior distributions using Monte Carlo Markov Chain methods. CASAL can project stock status into the future using deterministic or stochastic recruitment and can generate a number of yield measures commonly used in New Zealand stock assessment, including, Fmax, F0.1, and deterministic MSY.
A stock structure hypothesis considered sea floor features, presence and timing of spawning aggregations and length frequency of the catches. The catch history is well defined from 2002 onwards but is uncertain in 2000 and 2001 when a large number of non-CP vessels fished in the area. Ageing studies showed fish up to ~140 years to be present and most age classes were present. Eight acoustic survey biomass estimates were available from five different features collected from 2007 to 2015 during peak spawning. The model examined seven areas and did not indicate any poor fits. The results estimated that spawning stock biomass was above 50% of the virgin biomass for the base analysis. Projections of constant catch for the next 5 years at the 2017 catch level indicated that the median SS17 would not go below 50%. It was stressed that (a) stock structure remains uncertain and the SC should consider options for obtaining information to better support stock definitions; (b) age frequency data should be collected routinely; and (c), target strength remains uncertain.
The SC agreed that that the stock assessment could be used to provide advice to the Meeting of the Parties and that a Management Strategy Evaluation could be used to test different harvest strategies. It was noted that uncertainty in stock structure delineation existed and that the results are preliminary, based on the available information and expert judgement. It was agreed that genetic techniques should be explored to investigate stock structure.
Perversely, it was concluded that the EDSU mean and geostatistical variance should be adopted as used in current Australian and New Zealand stock assessments, though New Zealand does not always use this approach. Also, the net attached Acoustical Optical System should be used in areas of complex species mixing and or over steep slopes to reduce bias and sampling error. Of concern was that potential error in the target strength estimate could result in a bias of a factor of 2
Represents the interests of deep-sea fishing operators of the southern Indian Ocean by promoting responsible management of the fisheries of the SIO and the conservation of deep-sea biodiversity.