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Groundfish Conversion Factors

Two Monkfish lay on a measuring board.

The NEFSC Study Fleet Groundfish Conversion Factor Project was started to review and update current conversion factors used to calculate the total (round) weight from the graded weight of landed catch. 

The goal of the project is to examine the significance of variables such as time, space, sex and maturity and to determine if a model based approach is more appropriate than current static factors. 

After the catch is dumped on deck, individuals of the desired species are selected across the entire size range, if possible.  The length of the fish and round weight are recorded.  The fish is then dressed to the desired grade and weighed again.  The sex and reproductive stage of the fish are also recorded. 

Conversion factors are being calculated for Atlantic Cod (Gadus morphua), Haddock (Melanogrammus aeglefinus), Pollock (Pollachius virens), Goosefish (Lophius americanus) and Winter Skate (Leucoraja ocellata) with 397, 245, 34, 261 and 39 individuals examined respectively. 

Fish were sampled from the Gulf of Maine to the Southern New England. 

Round weight to gutted, head-on weight are calculated for gadids, round weight to wing weight are calculated for skate, and round weight to tail weight are calculated for goosefish.

Preliminary analyses for Atlantic Cod show that conversion factors vary over time with statistically significant differences in the mean individual based conversion factors (round weight/graded weight) across some months (Figure 2).  These differences in individual conversion factors affect the estimates of biomass removed during commercial fishing by month (Figure 3).

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