2008 Stock Assessment Update for Striped Mullet

Read the most current stock assessment for striped mullet in Florida, published December 2008.

Download the 2008 Stock Assessment Update for Striped Mullet Adobe PDF 

The 2008 Update of the Stock Assessment
for Striped Mullet, Mugil cephalus, in Florida

Florida Fish and Wildlife Conservation Commission
Fish and Wildlife Research Institute
100 Eighth Avenue Southeast 
St. Petersburg, FL 33701-5095

December 2008



Since the 1995 net ban, Florida’s commercial landings of striped mullet have sharply declined to an annual average of 8.0 million pounds, a 68% decline when compared to historical (1967-1990) average annual landings of 25 million pounds. The statewide commercial landings in 2007 were 6.5 million pounds, the lowest landings of the past ten years. The number of commercial fishing trips declined from an annual average of 60,331 trips before the net ban (1986-1994) to an annual average of 25,686 trips after the net ban (1995-2004), a 57% drop. The total number of fishing trips in 2007 was 20,063.

Standardized commercial catch rates for striped mullet increased following the elimination of entangling gears in Florida waters. This increase probably reflects the increase in the stock size.

The roe season (October-January) percentage of the total landings increased after the net ban on the southwest coast but remained unchanged on the east and northwest coasts. The average roe-season landings in the southwest region were 9.6 million pounds annually during 1986-1990, 6.6 million pounds annually during 1991-1994, and 3.4 million pounds annually during 1995-2007.

Statewide recreational landings estimates of striped mullet were variable without trend. During 2000-2007, recreational harvests averaged about 0.5 million pounds annually on the east coast, 0.4 million pounds annually on the northwest coast, and about 0.8 million pounds annually on the southwest coast.

Fishery-independent juvenile and adult survey data showed strong recruitment in 2006 in the central and northwest regions following the 2005 red tide events. This might reflect reduced predation pressure by large predators killed or displaced during the 2005 red tide.

The stock assessment utilized fishery-dependent and fishery-independent data sources (updated through 2007-08) and was based on three different assessment methodologies (non-equilibrium surplus production, statistical forward-projecting age structured, and statistical forward-projecting length-based).

A non-equilibrium, surplus production model (ASPIC) indicated that the F/Fmsy were consistently below 1 (0.45, 0.18, and 0.26 on the east, northwest, and southwest coasts, respectively) and the B/Bmsy were consistently above 1 (1.3, 1.5, and 1.4 on the east, northwest, and southwest coasts, respectively) after the net ban. The F/Fmsy and B/Bmsy ratios in more recent years suggest that the mullet stock is not considered to be overfished, nor is overfishing occurring in the three assessment regions.

Model base runs from the forward projecting age-structured model (ASAP) and forward projecting length-based model (SCALE) showed fishing mortality rates for striped mullet dropped sharply after the 1995 net ban from high levels in the early 1990’s in Florida. The fishing mortality rates (fully recruited F) dropped from 0.66-0.89 per year during 1992-1994 to 0.28-0.45 per year during 1995-2007 on the east coast; from 0.66-0.83 per year to 0.22-0.32 per on the northwest coast; and from 0.96-1.0 per year to 0.16-0.48 per year on the southwest coast.

The fishing mortality rates in more recent years (2005-2007) varied between 0.20 and 0.33 per year on the east coast, between 0.18 and 0.27 per year on the northwest, and between 0.16 and 0.31 per year on the southwest. These fishing mortality rates were below the F35% and F40% management reference points: F35%=0.67 and F40%=0.55 for the east coast; F35%=0.61 and F40%=0.51 for the northwest region; and F35%=0.55 and F40%=0.46 for the southwest region. In all three assessment region, transitional spawning potential ratios (tSPR) for striped mullet has trended upward, well above the 35% SPR target, in more recent years.

The current findings and the observed high tSPR estimates support the general conclusion that while there is uncertainty about the model output, the best estimates for the transitional spawning potential ratios in each region likely exceed the 35% SPR target. This seems to indicate that current levels of fishing effort are sustainable. Commercial landings levels in the past ten years and market condition suggest that landings have stabilized at about 1.3 million pounds on the east coast, 1.8 million pounds on the northwest coast, and 5.2 million pounds on the southwest coast. At these recent landings levels, fishing mortality rates should stabilize or decline further if growth of mullet stocks continue at the present rate.


Additional Information

The 2005 Update of the Stock Assessment for Striped Mullet, Mugil cephalus, in Florida Adobe PDF

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