Does the concept of spawning per recruit make sense?

Rochet, Marie-Joëlle

doi:10.1006/jmsc.2000.0803

Cited by 22 publications

(12 citation statements)

References 66 publications

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“…The compensatory nature of density-dependent growth implies that where the process is significant, yield and biomass responses to changes in exploitation are less pronounced than predicted from conventional dynamic pool models assuming density-independent growth (Beverton & Holt 1957;Rochet 2000). Hence disregarding density-dependent growth would lead to conservative reference points for underexploited stocks, but would give rise to over-optimistic assessments of the effectiveness of conservation measures for overexploited stocks.…”

Section: Discussionmentioning

confidence: 99%

Density-dependent growth as a key mechanism in the regulation of fish populations: evidence from among-population comparisons

Lorenzen

Enberg

2002

Proc. R. Soc. Lond. B

405

357

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It is generally assumed that fish populations are regulated primarily in the juvenile (pre-recruit) phase of the life cycle, although density dependence in growth and reproductive parameters within the recruited phase has been widely reported. Here we present evidence to suggest that density-dependent growth in the recruited phase is a key process in the regulation of many fish populations. We analyse 16 fish populations with long-term records of size-at-age and biomass data, and detect significant density-dependent growth in nine. Among-population comparisons show a close, inverse relationship between the estimated decline in asymptotic length per unit biomass density, and the long-term average biomass density of populations. A simple population model demonstrates that regulation by density-dependent growth alone is sufficient to generate the observed relationship. Density-dependent growth should be accounted for in fisheries' assessments, and the empirical relationship established here can provide indicative estimates of the density-dependent growth parameter where population-specific data are lacking.

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Section: Discussionmentioning

confidence: 99%

Density-dependent growth as a key mechanism in the regulation of fish populations: evidence from among-population comparisons

Lorenzen

Enberg

2002

Proc. R. Soc. Lond. B

405

357

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“…This threshold is typically included in the suite of biological reference points against which stock assessments are compared and is particularly useful in establishing thresholds protective of recruitment overfishing (Goodyear 1989;Murawski et al 2001;Fogarty and Gendron 2004). An important caveat in applying this reference point alone is the lack of inclusion of density-dependent changes in vital rates and recruitment (i.e., stock-recruitment relationships; Rochet 2000). To compute EPR, the value (E) of lifetime egg production under conditions of no exploitation is estimated as:…”

Section: Methodsmentioning

confidence: 99%

Influence of Skipped Spawning and Misspecified Reproductive Schedules on Biological Reference Points in Sustainable Fisheries

Secor

2008

Trans Am Fish Soc

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During the spawning season, adult striped bass Morone saxatilis can occur outside known spawning tributaries. This phenomenon has been observed in other fishes, suggesting that investigators have misspecified reproductive schedules by assuming annual spawning. Across a range of species, skipped (i.e., nonannual) spawning is positively correlated with longevity. Therefore, reproductive schedules that are misspecified due to skipped spawning or poorly known age at maturation are likely for many moderately to extremely long‐lived species. To explore the relevance of misspecified reproductive schedules on sustainable fisheries, a range of types of skipped spawning was modeled for the Chesapeake Bay striped bass population to test for effects on the biological reference point of egg production per recruit. The influence of misspecified reproductive rates was minor, particularly in relation to the effects of the two alternative size limits (46 and 71 cm) that are most commonly used in fisheries management. Among misspecification scenarios, reduced frequency of spawning later in life had the largest effect on reproductive rate. As fisheries management increasingly focuses on thresholds that promote resiliency, increased recognition of variation in reproductive schedules will probably place greater emphasis on conservation of age structure.

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“…It is worth pondering whether the wide range of F 30%SPR estimates observed in all models indicate true changes in resilience and, consequently, the need to change BRP when environment change, or whether it mostly indicates uncertainty of the estimate. Rochet (2000) has demonstrated that density dependent mechanisms in the adult population (e.g. growth rate, maturation schedule, fecundity, and egg size) may break down the proportionality between spawning stock biomass and recruitment making spawning per recruit an ambiguous concept.…”

Section: Discussionmentioning

confidence: 99%

Modelling the effect of ecosystem change on spawning per recruit of Baltic herring

Rahikainen

Kuikka²,

Parmanne³

2003

ICES Journal of Marine Science

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A plea for linking assessment and management to the broader ecosystem state has been made several times in the fisheries literature. The need for ecosystem considerations is obvious for Baltic herring stock which has experienced large fluctuations in growth and natural mortality rate. Biological reference points, based on stock-recruitment data, have gained importance under precautionary approach and the need for more restrictive management. An alternative method for establishing thresholds for recruitment overfishing is spawning per recruit analysis. Within this context, understanding the effects of highly variable natural mortality and growth rate on fishing mortality reference point is of interest. We used Monte Carlo simulations to investigate variation in spawning per recruit caused by varying stock attributes. Causal biological response to changing environmental conditions was created by adjusting the correlation between growth, maturity, and natural mortality. The correlation of the input variables was controlled under three models, assuming future conditions were (1) as experienced recently (empirical model), (2) random, and (3) depending upon causal linkages in the biological key processes (ecological model). The overall uncertainty was large in all models. Biological reference point (F 30%SPR ) was uncertain due to problem of defining maximum spawning per recruit and due to variation in input variables in SPR analysis. The concept of F x%SPR was judged to be ambiguous. The use of causal ecological knowledge reduced uncertainty of the reference point only to a limited extent. However, relying only to the observed data appeared to be the riskiest approach.

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Does the concept of spawning per recruit make sense?

Cited by 22 publications

References 66 publications

Density-dependent growth as a key mechanism in the regulation of fish populations: evidence from among-population comparisons

Density-dependent growth as a key mechanism in the regulation of fish populations: evidence from among-population comparisons

Influence of Skipped Spawning and Misspecified Reproductive Schedules on Biological Reference Points in Sustainable Fisheries

Modelling the effect of ecosystem change on spawning per recruit of Baltic herring

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