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.

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.

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.

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.

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.

The influence of forage fish abundance on the aggregation of Gulf of Maine Atlantic cod (Gadus morhua) and their catchability in the fishery

2014 ◽  
Vol 71 (9) ◽  
pp. 1349-1362 ◽  
Author(s):  
David E. Richardson ◽  
Michael C. Palmer ◽  
Brian E. Smith
Keyword(s):  
Gadus Morhua ◽  
Gulf Of Maine ◽  
Atlantic Cod ◽  
Distribution Patterns ◽  
Fish Populations ◽  
Dependent Data ◽  
Forage Fish ◽  
Catch Per Unit Effort ◽  
Sand Lance ◽  
Unit Effort

Shifts in the distribution and aggregation patterns of exploited fish populations can affect the behavior and success of fishermen and can complicate the interpretation of fisheries-dependent data. Starting in 2006, coinciding with an increase in sand lance (Ammodytes spp.) abundance, Gulf of Maine Atlantic cod (Gadus morhua) concentrated on Stellwagen Bank, a small (405 km2) underwater plateau located in the southwestern portion of the larger (52 461 km2) stock area. The cod fishery in turn concentrated on Stellwagen Bank. Specifically, the proportion of Gulf of Maine cod landings caught in a single 10-minute square area (260 km2) encompassing the tip of Stellwagen Bank increased from 12% in 2005 to 45% in 2010. An increase in landings per unit effort in the fishery coincided with the concentration of the fleet on Stellwagen Bank. Overall, both fisheries-independent and fisheries-dependent data indicate that an increase in sand lance abundance resulted in cod aggregating in a small and predictable area where they were easily caught by the fishery. More broadly, this work illustrates how changes in the distribution patterns of fish and fisherman can decouple trends in abundance and fisheries catch per unit effort.

scholarly journals Is recovery of northern cod limited by poor feeding? The capelin hypothesis revisited

2014 ◽  
Vol 71 (4) ◽  
pp. 784-793 ◽  
Author(s):  
Darrell R. J. Mullowney ◽  
George A. Rose
Keyword(s):  
Newfoundland And Labrador ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Wild Fish ◽  
Fish Growth ◽  
Small Fish ◽  
Performance Trends ◽  
Northern Cod ◽  
Capelin Mallotus Villosus ◽  
Prime Condition

Abstract The slow recovery of the “northern” Atlantic cod (Gadus morhua) stock off Newfoundland and Labrador has been ascribed to many factors. One hypothesis is poor feeding and condition as a consequence of a decline in capelin (Mallotus villosus), their former main prey. We compared the growth and condition of cod from known inshore (Smith Sound) and offshore (Bonavista Corridor) centres of rebuilding in wild subjects versus captive subjects fed an unlimited diet of oily rich fish. Wild fish in these areas have had different diets and population performance trends since stock declines in the early 1990s. Captive cod from both areas grew at the same rates and achieved equivalent prime condition, while their wild counterparts differed, with smaller sizes, lower condition in small fish, and elevated mortality levels in the offshore centre. Environmental temperature conditions did not account for the differences in performance of wild fish. Our results suggest that fish growth and condition, and hence rebuilding in the formerly large offshore spawning components of the northern cod, have been limited by a lack of capelin in their diet. Furthermore, we suggest that these groups are unlikely to rebuild until a recovery in capelin occurs.

scholarly journals Direct and indirect effects of minke whale abundance on cod and herring fisheries: A scenario experiment for the Greater Barents Sea

2000 ◽  
Vol 2 ◽  
pp. 120 ◽  
Author(s):  
Tore Schweder ◽  
Gro S Hagen ◽  
Einar Hatlebakk
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Minke Whale ◽  
Clupea Harengus ◽  
Prey Abundance ◽  
Balaenoptera Acutorostrata ◽  
Time Step ◽  
Minke Whales ◽  
Spawning Stock ◽  
Capelin Mallotus Villosus

To study the pattern of interaction between minke whale (Balaenoptera acutorostrata) abundance and the main fisheries in the Greater Barents Sea, a simulation experiment was carried out. The population model involves 4 species interconnected in a food web: cod (Gadus morhua), capelin (Mallotus villosus), herring (Clupea harengus) and minke whales. Minke whales are preying on cod, capelin andherring; cod are preying on (young) cod, capelin and herring; herring in the Barents Sea are preying on capelin; while capelin is a bottom prey in the model. The consumption function for minke whales is non-linear in available prey abundance, and is estimated from stomach content data and prey abundance data. The model is dynamic, with a time step of one month, and there are two areas: the BarentsSea and the Norwegian Sea. Minke whale abundances are kept on fixed levels, while recruitment in fish is stochastic.Cod and herring fisheries are managed by quotas targeting fixed fishing mortalities, while capelin is managed with a view to allow the cod to have enough food and leaving a sufficient spawning stock of capelin. The model is simulated over a period of 100 years for a number of fixed levels of minke whaleabundance, and simulated catches of cod, herring and capelin are recorded.The experiment showed interactions between whale abundance and fish catches to be mainly linear. For cod catches, both the direct effect of whales consuming cod, and the indirect effect due to whales competing with cod for food and otherwise altering the ecosystem, are linear and of equal importance. The net effect on the herring fishery is of the same magnitude as the net effect on the cod fishery, witheach extra whale reducing the catches of both species by some 5 tonnes. These conclusions are conditional on the model and its parameterisation.

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