Extending time series of fish biomasses using a ­simple surplus production-based approach

Abstract

Long time series of fish biomasses are needed in order to understand the changes in marine ecosystems and to set appropriate targets for their management and conservation. Fish biomasses from stock assessments usually cover only the recent 3 to 4 decades, and extending these time series using conventional data-demanding methods will, for many stocks, likely not be possible due to limited historical data. However, catch data are usually available for several decades longer than stock assessments. In the present study, we show that catch data, combined with information on average surplus production rate (SPR), of a stock could be used to derive proxies for pre-assessment biomasses. The sensitivity of biomass estimates to different SPR values was explored using data on 55 stocks from different taxa in the North Atlantic. The time series of biomasses estimated from the assessments could, for most stocks, be reconstructed by applying average stock-specific SPR values for all years, i.e. neglecting inter-annual variability in SPR. The approach of applying the information on SPR from the assessment period to pre-assessment years performed reasonably well in extending the biomass time series by 2 to 6 decades for 5 out of 6 stocks used as test cases. Density dependence and major climate variations were taken into account where such effects on SPR were expected. The main challenge for the approach appeared to be long-term changes in productivity regimes. The apparently consistent average SPR among stocks of a similar species could also facilitate use of the SPR-based approach to derive biomass estimates in contemporary data-poor situations.

Assembly rules for aggregate-species production models: simulations in support of management strategy evaluation

“…Fuller consideration of this interaction seems warranted (Tyrrell et al 2011), and could be simulated using larger datasets of species productivity (e.g. Walters et al 2008, Eero & MacKenzie 2011.…”

Extension of biomass estimates to pre-assessment periods using density dependent surplus production approach

“…The surplus production rate in year y is defined as: where B is biomass and C is catch volume. Eero and MacKenzie [ 12 ] reformulated this equation as replacing the time dependent SPR y by its average, SPR. Next, they applied Eq (2) to reconstruct stock biomass for years not covered by the analytical stock assessment using only total catch data and the SPR, estimated from the available assessment.…”

“…Eero and MacKenzie [ 12 ] presented a simple method for biomass reconstruction in the pre-assessment period using catch volume only in that period and analytical assessment results from later years. They used the concept of the surplus production rate (SPR).…”

“…The SPR is calculated using catch volumes and biomass estimated by analytical stock assessment and is used as an average in backward biomass recalculations. However, the analysis provided by Eero and MacKenzie [ 12 ] indicates that for some stocks, the SPR showed significant variation over time. In fact, the SPR may be dependent on stock biomass because at high biomass of a stock, the surplus production is usually low, while it is much higher when biomass of stock is low.…”

Nineteenth century narratives reveal historic catch rates for Australian snapper (Pagrus auratus)

“…Many marine fisheries have been intensively exploited for generations, yet detailed fisheries data rarely extend further than three or four decades into the past (Eero and MacKenzie ). Lack of data from the developmental stages of a fishery is problematic for stock assessment and can lead to bias in estimates of key parameters, both in quantities relating to the productivity of the stock and in those responsible for its potential overall magnitude.…”