The environmental impact of Atlantic co
d (Ga
dus morhua L.) farming was quantifie
d by assessing the benthic effects of a large co
d farm in Shetlan
d, UK an
d by parameterising a mathematical mo
del base
d on an existing salmon mo
del (DEPOMOD, [Cromey, C.J.,
Nickell, T.D., Black, K.D., 2002a. DEPOMOD—Mo
delling the
deposition an
d biological effects of waste soli
ds from marine cage farms. Aquaculture 214, 211–239.]) to pre
dict soli
ds
deposition from farme
d co
d to the seabe
d. Benthic physico-chemical an
d macrofaunal
data for three consecutive years provi
de
d synoptic
data for mo
del vali
dation, allowing mo
del testing throughout the growing cycle, from low biomass to near maximum. A vi
deo technique for quantifying the particle size an
d settling rates of co
d faeces was further
develope
d (weighte
d mean settling velocity for co
d faeces was 3.7 cm s
− 1), an
d faecal output experiments yiel
de
d temporal
data on post-pran
dial faecal output (faecal output was 8.5 % of fee
d input
d− 1 by mass), which was lower than faecal output rates that have been use
d in mo
delling salmon impacts. Fee
d settling experiments showe
d large an
d significant
differences between three proprietary co
d fee
ds.
At most benthic stations, there was a good fit between modelled and measured benthic Infaunal Trophic Index (ITI) but it failed to reproduce the moderate to heavy impact observed at an inshore transect. Possible reasons for the underperformance of the model in this area include the hydrographic data available and unreported cage movements in the area of the transect. When these factors were taken into account in the model, performance improved.
Surveys of the sea bed surrounding the cod farm indicated that over a cod growing cycle up to near maximum biomass, there is a biological response to organic enrichment of the near-field sediments. This enrichment is not excessive in terms of the biomass present, and is comparable to salmon culture sites of similar scale in similar environments. Provided that species-specific parameters are used for particulate wastes no special considerations for modelling of this relatively new aquaculture species are necessary.