Publication Date:
2013-12-17
Description:
Indicators and reference points for assessing the good environmental status of commercially exploited marine fishes and invertebrates are presented, using 20 stocks from the German exclusive economic zone. New estimates of length-weight relationship, von Bertalanffy growth, length at 50% and 90% maturity, age at 50% maturity, and length and age where cohort biomass is maximum are presented for each stock. Twice the stock size below which recruitment may become impaired (SSBpa) is proposed as a proxy for the biomass that can produce the maximum sustainable yield, which is the lower limit reference point for stock size. A rule-based hockey stick function is presented to estimate SSBpa from stock-recruitment data. The rate of natural mortality is proposed as an upper limit reference point for fishing mortality. The length where 90% of females have reached sexual maturity is proposed as a lower limit reference point for mean length of fishes in commercial catches. The length where cohort biomass is maximum and where therefore a given catch has the least impact on the age structure of the stock is recommended as target length in commercial catches. A new large fish indicator (LFIS) is developed as the ratio of large fish biomass to mature fish biomass. The corresponding upper limit reference point is the ratio of large fish that would be present with fishing mortality equal to natural mortality. Survey data are used to establish proxies for above indicators and reference points for data-poor stocks. Applying the data-poor methods to fully assessed stocks and comparing the resulting scores for good environmental status show good agreement. Data, spread sheets and R-code used in this study are available online.
Type:
Report
,
NonPeerReviewed
Format:
text
Format:
archive
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