When is Spawning Biomass a Good Proxy for Stock Reproductive Potential? A Case Study of Red Snapper (Lutjanus campechanus) in the Gulf of Mexico SEFSC Clay E. Porch and Gary. R. Fitzhugh American Fisheries Society Portland, Oregon August 2015 Illustration: Diane Rome Peebles

Impetus Stock assessments often use mature biomass to measure reproductive potential But…egg production is seldom proportional to somatic growth Weight = aL3 Eggs = bL4-5

Gulf of Mexico Red Snapper are like that Batch fecundity ( = aL 4.2 )

Gulf of Mexico Red Snapper also spawn more often with age Porch et al. 2015. Marine and Coastal Fisheries.

many fish are immature during the period of fast somatic growth after maturity, gains in egg production faster than gains in weight

Per capita reproductive potential of red snapper measured in weight and eggs

Total reproductive potential of red snapper measured in weight and eggs (at MSY)

So what? THE RED SNAPPER POPULATION IS THIS BIG SPORT FISHERMEN FISHERIES SCIENTISTS

Trends in spawning indicators over time

Trends in spawning indicators over time *Rescaled to mean 1986-2010

Spawning potential equilibrium reference points

Perceived spawner-recruit relationship

Example 1: True h = 0.7 additive error

Example 2: True h = 0.7 additive error No observations at large stock sizes

Example 3: True h = 0.7 multiplicative error

Conclusions w.r.t. stock assessments Mature number is poor proxy for red snapper spawning Mature biomass may not be too bad for fish like red snapper Underestimates steepness (= fish less) Over-estimates contribution of young fish (= fish more) SPR reference points overestimated by up to 40% (for low targets) There may be other important age/size dependent factors like egg quality spawning locations

Conclusions w.r.t. stock assessments Mature number is poor proxy for red snapper spawning Mature biomass may not be far off for fish like red snapper Underestimates steepness (= fish less) Over-estimates contribution of young fish (= fish more) SPR reference points overestimated by up to 40% (for low targets) From a stock assessment perspective, for species where reproductive capacity is unknown, first priority should be placed on determining maturity (which is cheap anyway) But still important to pursue quantifying egg production, especially for species where reference points are proposed with corresponding SPR’s below 40%

Pensacola red snapper fishery Questions? Pensacola red snapper fishery 1940s Photo credit: Pensacola News Journal http://archive.pnj.com/apps/pbcs.dll/gallery

Stock-recruitment relationship