Predator Stomachs as Sampling Tools for Prey Distribution: Atlantic Cod (Gadus morhua) and Capelin (Mallotus villosus)

1993 ◽  
Vol 50 (7) ◽  
pp. 1541-1547 ◽  
Author(s):  
Lenore Fahrig ◽  
George R. Lilly ◽  
Daniel S. Miller
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stomach Contents ◽  
Mallotus Villosus ◽  
Predator Prey ◽  
Prey Distribution ◽  
Capelin Mallotus Villosus ◽  
Negative Effect ◽  
Predator Abundance ◽  
Bottom Depth

We demonstrate a direct relationship between the amount of prey (capelin, Mallotus villosus) in its predators' stomachs (Atlantic cod, Gadus morhua) and the biomass of the prey in the same localities. The relationship at a local scale implies that predator stomach contents can be used to estimate prey distribution. There is no evidence for either (1) a negative effect of local predator abundance on stomach contents (expected if local prey depletion and/or feeding interference occurs when predator density is high) or (2) a negative effect of the amount of other food in cod stomachs on the amount of capelin in the stomachs (expected if prey switching occurs). There is a negative effect of bottom depth on amount of capelin in cod stomachs as expected, since capelin are pelagic and cod are primarily bottom-dwelling, resulting in less vertical overlap between the species in deep water. This type of analysis may be useful in other predator–prey systems. Simultaneous stomach samples and independent biomass estimates of the prey are required, but once the model is built, it permits estimation of prey distribution in places and times when no direct survey of the prey can be done.

Potential contact statistics for measuring scale-dependent spatial pattern and association: an example of northern cod (Gadus morhua) and capelin (Mallotus villosus)

2000 ◽  
Vol 57 (7) ◽  
pp. 1355-1368 ◽  
Author(s):  
Richard L O'Driscoll ◽  
David C Schneider ◽  
George A Rose ◽  
George R Lilly
Keyword(s):  
Spatial Distribution ◽  
Spatial Pattern ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Simulated Data ◽  
Point Pattern Analysis ◽  
Point Pattern ◽  
Mallotus Villosus ◽  
Capelin Mallotus Villosus ◽  
Potential Contact

Analysis of simulated data showed that potential contact statistics could be used to describe spatial pattern in sample density data. Potential contact is a new method, analogous to Ripley's K function for mapped point pattern analysis. Potential contact can be used to describe spatial pattern and association over a range of scales without grouping data and is robust against the presence of zeros. The statistical output is ecologically interpretable, as a measure of the degree of contact between individuals. This new technique was applied to examine changes in the spatial distribution of Atlantic cod (Gadus morhua) off Newfoundland, Canada, from 1985 to 1994, a period that encompassed a collapse of the cod stock. Sample data from bottom-trawl surveys indicated that cod were aggregated in patches with dimensions of 100-250 km. During the period of cod decline in the 1990s, spatial structure changed in three ways: the number of patches decreased, patch size shrank, and contact with conspecifics at small (10-20 km) scales fell. Cod were broadly associated with capelin (Mallotus villosus), a major prey species. Spatial distribution of capelin changed over the same time period as changes in cod distribution, and there was no evidence that contact between cod and capelin decreased.

Effects of predation from pelagic 0-group cod (Gadus morhua) on mortality rates of capelin (Mallotus villosus) larvae in the Barents Sea

2007 ◽  
Vol 64 (12) ◽  
pp. 1710-1722 ◽  
Author(s):  
Elvar H Hallfredsson ◽  
Torstein Pedersen
Keyword(s):  
Mortality Rate ◽  
Stomach Content ◽  
Gadus Morhua ◽  
Barents Sea ◽  
Stomach Contents ◽  
Mortality Rates ◽  
Mallotus Villosus ◽  
The Barents Sea ◽  
Predation Mortality ◽  
Capelin Mallotus Villosus

Surveys were carried out in 2002 and 2003 to test whether predation from pelagic 0-group cod (Gadus morhua) juveniles affects mortality rates of Barents Sea capelin (Mallotus villosus) larvae. In 2002, capelin larvae were observed in 17% of the cod stomachs and predation was observed at 19 of 50 stations. In 2003, capelin larvae were observed in 8% of the cod stomachs and predation was observed at 19 of 37 stations. The stomach contents and zooplankton samples were dominated by copepods and krill. The number of capelin larvae in cod stomachs increased with increasing capelin larvae abundance and cod length and decreased with increasing stomach content of copepods and prey abundance of krill. The time when capelin larvae could be recognised after ingestion in the cod stomachs was estimated experimentally and depended on predator and prey lengths. The estimated overall predation mortality rate from juvenile cod on capelin larvae was about 1.5% per day for both years and can potentially have a significant effect on the survival of capelin larvae, depending on the overlap in the different years.

Interactive Effects of Geophysically-Forced Sea Temperatures and Prey Abundance on Mesoscale Coastal Distributions of a Marine Predator, Atlantic Cod (Gadus morhua)

1989 ◽  
Vol 46 (11) ◽  
pp. 1904-1913 ◽  
Author(s):  
G. A. Rose ◽  
W. C. Leggett
Keyword(s):  
Coastal Zone ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Distribution Patterns ◽  
Prey Abundance ◽  
Interactive Effects ◽  
Mallotus Villosus ◽  
Sea Temperature ◽  
Marine Predator ◽  
Capelin Mallotus Villosus

Geophysically-forced sea temperatures and prey abundance interactively regulated mesoscale (10's to 100's of km) inshore Atlantic Cod (Gadus morhua) distribution patterns in the northeastern Gulf of St. Lawrence, in both 1985 and 1986. Cod were located most often at temperatures within the range 0–5 °C. However, when mean densities of their chief prey (capelin, Mallotus villosus) were high (> 100/105m3) within the coastal zone, cod frequented waters having temperatures similar to those at which this prey were aggregated, within the broader range of temperatures −0.5 to 8.5 °C. The proportions of cod occupying sea temperature strata were significantly and positively correlated with those of capelin (r = 0.64, slope = 0.6, df = 86), in both 1985 and 1986, under two conditions: (1) sea temperatures within the range 1–9 °C; and (2) mean capelin densities > 100/105m3. Under conditions of lower mean capelin densities, cod distributions were independent of those of capelin. At temperatures outside the range 1–9 °C, cod and capelin densities were not correlated, regardless of capelin densities.

A model for estimating meal frequency and meal size from stomach data with an application to Atlantic cod (Gadus morhua) feeding on capelin (Mallotus villosus)

1997 ◽  
Vol 54 (4) ◽  
pp. 876-889 ◽  
Author(s):  
K G Magnússon ◽  
T Aspelund
Keyword(s):  
Gadus Morhua ◽  
Negative Binomial ◽  
Atlantic Cod ◽  
Random Variable ◽  
Meal Size ◽  
Meal Frequency ◽  
Mallotus Villosus ◽  
Method Of Maximum Likelihood ◽  
Capelin Mallotus Villosus ◽  
Prey Items

The feeding of a predator on prey that occurs in schools is modelled as a stochastic process involving two random variables: (i) the number of schools that the predator finds per unit time and (ii) the number of prey items captured in each encounter. The number of encounters is governed by a Poisson process and the number of prey items can be either a Poisson random variable or more generally a negative binomial. The principal parameters in the model can be interpreted as the average meal frequency and the average meal size. This model is applied to Atlantic cod (Gadus morhua) feeding on capelin (Mallotus villosus). Cod stomachs from six length-groups were sampled off eastern Iceland and the number of capelin in individual stomachs recorded. The parameters in the stochastic feeding model are estimated by the method of maximum likelihood using the observed frequency distribution of capelin numbers in cod stomachs. The data fit the model well where the meal size is modelled by a negative binomial distribution, but less successfully where the meal size has a Poisson distribution. Finally, using the estimates of average meal frequency and average meal size the average and the standard deviation of consumption rate are calculated.

Diet of harp seals (Phoca groenlandica) in nearshore waters of the northwest Atlantic during 1990 – 1993

1995 ◽  
Vol 73 (10) ◽  
pp. 1805-1818 ◽  
Author(s):  
John W. Lawson ◽  
Garry B. Stenson ◽  
Dave G. McKinnon
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stomach Contents ◽  
Clupea Harengus ◽  
Relative Importance ◽  
Northwest Atlantic ◽  
Arctic Cod ◽  
Diet Diversity ◽  
Phoca Groenlandica ◽  
Capelin Mallotus Villosus

The nearshore diet of northwest Atlantic harp seals (Phoca groenlandica) was determined by reconstructing the contents of 1167 prey-containing stomachs (78.3% of 1490) collected from 1990 to 1993. Although harp seals consumed at least 62 species, 6 accounted for most of the mass consumed and their relative importance varied by area. Based on percent wet mass, sculpins (Cottidae) and Arctic cod (Boreogadus saida) were the main components of the diet of older seals (> 1 year old) off Labrador, whereas Arctic cod and Atlantic herring (Clupea harengus) were the main prey of seals from northeastern Newfoundland. A more diverse diet was observed in seals taken off the west coast of Newfoundland, where capelin (Mallotus villosus), herring, Atlantic cod (Gadus morhua), redfish (Sebastes spp.), and Arctic cod were the main species. Redfish and Atlantic cod were important to seals along the south coast of Newfoundland. Eighty percent of fish consumed were less than 18 cm long, smaller than those taken by commercial fisheries. Pups (less than 1 year old) consumed fewer and smaller prey of a less varied assortment. Annual and seasonal variation in the diets was observed in the collection from northeastern Newfoundland. Arctic cod was the major prey consumed throughout the year by seals of all ages, although the relative importance of herring, capelin, and squid (Teuthoidea) increased during the summer. Invertebrates and capelin made up a greater proportion of the diet in 1992, owing to a decline in consumption of Arctic cod. This finding was associated with a decrease in the mass of stomach contents. Diet diversity did not change significantly over the study period.

scholarly journals Bottom-up limits to Newfoundland capelin (Mallotus villosus) rebuilding: the euphausiid hypothesis

2013 ◽  
Vol 71 (4) ◽  
pp. 775-783 ◽  
Author(s):  
Shannon G. Obradovich ◽  
Erin H. Carruthers ◽  
George A. Rose
Keyword(s):  
Newfoundland And Labrador ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Mallotus Villosus ◽  
Bottom Up ◽  
Grand Banks ◽  
Capelin Mallotus Villosus ◽  
Dietary Component ◽  
Δ 15N ◽  
Δ15n And Δ13c

Abstract Capelin (Mallotus villosus) is the key forage fish species in the Newfoundland and Labrador Shelf ecosystem. Capelin stocks collapsed in the early 1990s, concurrent with declines in “northern” Atlantic cod, Gadus morhua. Neither has fully recovered yet. Changes in growth, condition, and behaviour accompanied capelin declines on the northern Grand Banks (NGB), and remain two decades later. Feeding, growth, and condition of NGB capelin were all lower when compared with capelin from the eastern Scotian Shelf (ESS), where abundance increased following predator declines. For age 2–5 capelin of both sexes, all but one of five comparable age–sex groups were significantly larger on the ESS (e.g. age 3 females average 169 mm on the ESS and 151 mm on the NGB). Neither temperature nor density-dependence explain these differences. However, dietary differences were prominent. ESS capelin had higher total fullness indices (TFIs) than NGB fish at all sizes [mean TFIESS = 1.43 (± 1.14), mean TFINGB = 0.48 (± 0.70)]. Euphausiids (especially Thysanoessa spp.) were a main dietary component on the ESS but not on the NGB. Stable isotope analyses (δ15N and δ13C) for NGB capelin also indicated few dietary euphausiids. Trophic fractionation of δ 15N was 4.740/00, suggesting NGB capelin were food limited. Capelin recovery on the Newfoundland and Labrador Shelf appears limited by bottom-up forcing, in particular lack of euphausiid prey.

Seasonal Variation in the Diet of Harp Seals (Phoca groenlandica) from the Gulf of St. Lawrence and Western Hudson Strait

1993 ◽  
Vol 50 (7) ◽  
pp. 1363-1371 ◽  
Author(s):  
Gregor Gilpin Beck ◽  
Michael O. Hammill ◽  
Thomas G. Smith
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stomach Contents ◽  
Fish Prey ◽  
Lawrence Estuary ◽  
Phoca Groenlandica ◽  
Capelin Mallotus Villosus ◽  
Gross Energy ◽  
St Lawrence Estuary ◽  
Magdalen Islands

Of 247 harp seal (Phoca groenlandica) stomachs collected between December 1988 and October 1990 from western Hudson Strait (autumn), the northern Gulf of St. Lawrence (December), the St. Lawrence estuary (winter and April), and the Magdalen Islands (March), 140 (57%) contained food. The Magdalen Islands sample contained significantly more empty stomachs (62%, n = 164) than those from all other locations. Both the unreconstructed mass of stomach contents and the proportion of fish and invertebrate prey within individual stomachs varied significantly with location and season. Harp seals obtained from the northern Gulf of St. Lawrence during their southward migration fed less intensively, and on a wider variety of both invertebrate and fish prey, notably Parathemisto libellula, Pandalus sp., sand lance (Ammodytes sp.), and Atlantic cod (Gadus morhua). Feeding was more intensive and specialized in Hudson Strait and the St. Lawrence estuary where capelin (Mallotus villosus) dominated in the diet. Capelin contributed 89 and 98% of gross energy in samples from Hudson Strait (1990) and the estuary (April). The number of capelin per stomach consumed by seals from the St. Lawrence estuary in April was high (169.4 ± 58.9, mean ± SD, n = 9). The mean estimated lengths of capelin and cod consumed were 132 and 140 mm.

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