1999 SI Meeting Presentation

[Towards] estimates of broad-scale predation mortality

L. P. Madin, E. F. Horgan, H. Franklin, S. M. Bollens, and B. K. Sullivan

Mortality due to predation by invertebrates and fishes is expected to be a significant loss term for target species on Georges Bank. The overall objective of our proposed research is to collect and analyze the data required to make a quantitative assessment of time- and site-specific predation mortality on populations of the target species. Our approach combines information on the abundance and co-occurrence of predators and target prey species on Georges Bank, derived from the continuing Broad Scale Survey, with new data on feeding specificity and rates of the principal predator species. We have identified at total of 19 fish and invertebrate predator species (Table) and have obtained feeding rate a selectivity data for them, either from our own experimental or observational work, from the literature, or by estimation on energetic grounds. We have begun to combine feeding rates for specific predator-prey combinations with their distributions on Georges Bank in order to map predation mortality in time and space, using the following protocol:

Plot bank-wide (depth-stratified) abundance map for each predator (#/m^-2) from MOC-1 and/or MOC-10 data.
Introduce station- and depth-specific abundance of prey categories (e.g. total copepods).
Combine predator abundance with feeding rate (fixed or functional response) to calculate "Potential Predator Impact" or PPI (# prey eaten m^-2 d^-1) for each station and depth.
Adjust PPI with appropriate Q₁₀ to calculate temperature-dependent PPI
Adjust t-dependent PPI for target prey type (if there is a positive or negative selection for target species) to give # target prey eaten m^-2 d^-1
Divide by abundance of target species to calculate "Instantaneous Mortality" or IM of target species (fraction eaten m^-2 d^-1).
Sum IM values of all co-occuring predators for estimate of total IM for each target species.

Using Matlab and Easy-Krig routines, these specific predation impacts can be combined to estimate total mortality due to predation for each target species as a function of location, season and year.

Table of Georges Bank predators, prey and feeding data:

Predator Occurrence Prey Feeding Data

Cnidarians
Clytia gracilis (hydroids)	Often very abundant on crest	Nauplii, copepods, fish larvae	F, T responses, selectivity on copepod eggs & nauplii, rates on cod larvae (GLOBEC data)
Cyanea capillata	Patchy occurrence	Copepods, fish eggs	Rates, selectivity on copepods (literature data)
Obelia sp.	Extremely abundant at times	Nauplii	F response on nauplii from experiments (GLOBEC data)
Other hydromedusae	Variable occurrence, rarely dense	Copepods, Fish larvae	Rates on fish larvae from gut contents, experiments (literature data)
Nanomia cara	Very patchy occurrence, dense clusters	Copepods	Rates on copepods from gut contents (literature data)
Ctenophores
Bolinopsis infundibulum	Patchily abundant on flank, hard to quantify	Copepods, Fish larvae	Rates on copepods from gut contents (GLOBEC data)
Pleurobrachia pileus	Patchily abundant in spring	Copepods fish larvae	Rates on copepods from gut contents (GLOBEC data), F and T responses (literature data)
Chaetognaths
Sagitta spp.	Fairly uniform abundances	Copepods	F, T responses on copepods (literature data)
Copepods
Centropages spp.	Very abundant on crest	Nauplii	F, T responses, selectivity on nauplii (GLOBEC data)
Metridia lucens	Year round on crest	Nauplii	F, T responses, selectivity on nauplii (GLOBEC data)
Temora longicornis	Winter and spring	Nauplii	F, T responses, selectivity on nauplii (GLOBEC data)
Mysids
Neomysis americana	Patchily abundant on crest	Copepods	F response on copepods (literature data)
Euphausiids
Meganyctiphanes norvegica	Patchily abundant, north flank	Copepods	Rates on Calanus, Pcal. (GLOBEC and literature data)
Nematoscelis spp.	Patchily abundant	Copepods	Estimate from other species (literature data)
Euphausii krohnii	Patchily abundant	Copepods Fish larvae	Estimate from other species (literature data)
Amphipods
Themisto gaudichaudii	Patchy, but adults or juveniles often abundant	Nauplii, copepods	Rates on copepods, nauplii from gut contents (GLOBEC data), F,T responses (literature data)
Isopods
Cirolana polita	Demersal, in water column at night	Copepods, Larval fish ?	Rates on nauplii, copepods from experiments (GLOBEC data)
Fishes
Clupea harengus	Briefly abundant during migratory passage	Copepods, larval fish	Rates on copepods, fish larvae from gut contents (COP-GLOBEC data),
Scomber scombrus	Briefly abundant during migratory passage	Copepods, larval fish	Rates on copepods, fish larvae from gut contents (COP-GLOBEC data),