Species and size differences in the digestion of otoliths and beaks: implications for estimates of pinniped diet composition

1997 ◽  
Vol 54 (1) ◽  
pp. 105-119 ◽  
Author(s):  
D J Tollit ◽  
M J Steward ◽  
P M Thompson ◽  
G J Pierce ◽  
M B Santos ◽  
...  
Keyword(s):  
Confidence Intervals ◽  
North Sea ◽  
Diet Composition ◽  
Prey Size ◽  
Phoca Vitulina ◽  
Correction Factors ◽  
Fish Size ◽  
Harbour Seals ◽  
Specific Correction ◽  
Length Reduction

We examined the digestion of hard remains of between one and four different size ranges of nine key North Sea prey taxa fed to seven captive harbour seals (Phoca vitulina). Percentage length reduction (mean 27.5%) and recovery rates (mean 42%) of experimental otoliths varied between species and were positively correlated to fish size and otolith robustness (mass/length). Mean length reduction of egested otoliths increased systematically with increasing size of ingested whiting and sandeel otoliths (p < 0.001), indicating that the size of larger fish may be underestimated. Intraspecific variation in otolith digestion was high (CV = 0.48-1.30), and to control for the artificial conditions of a captive study, external morphological features of otoliths were used to grade the degree of digestion and provide grade-specific correction factors. Bootstrap simulations were used to estimate 95% confidence intervals around correction factors and when partitioned indicated that calculation errors were in general less important than resampling errors. The application of species-, size-, and grade-specific correction factors progressively improved reconstructed estimates of prey biomass fed. As a consequence, estimates of prey size and diet composition require otoliths from faeces to be graded and more complex correction factors applied.

Prey selection by harbour seals, Phoca vitulina, in relation to variations in prey abundance

1997 ◽  
Vol 75 (9) ◽  
pp. 1508-1518 ◽  
Author(s):  
Dominic J. Tollit ◽  
Paul M. Thompson ◽  
Simon P. R. Greenstreet
Keyword(s):  
Diet Composition ◽  
Prey Size ◽  
Prey Selection ◽  
Phoca Vitulina ◽  
Correction Factors ◽  
Fish Prey ◽  
Size Selection ◽  
Harbour Seals ◽  
Moray Firth ◽  
Time Periods

This study compared the composition of the diet of harbour seals (Phoca vitulina) feeding in the Moray Firth, Scotland, with the abundance of their fish prey estimated from dedicated fishery surveys in January 1992 and 1994 and June 1992. Prey-size selection was also examined in these three time periods and in January 1991. In each period, the most abundant fish species contributed most to the diet. However, the relative abundances of the remaining species in the sea showed little similarity to their contribution to the seals' diet. Diet composition was almost totally dominated by either pelagic species or species dwelling on or strongly associated with the seabed, depending upon the relative abundance of pelagic schooling prey. Most fish consumed were 10–16 cm in length, although larger cod and herring were taken. With the exception of cod, the extent of size selection was dependent upon the use of correction factors that accounted for otolith erosion due to digestion.

Diet of harbour seals at Mousa, Shetland, during the third quarter of 1994

1997 ◽  
Vol 77 (2) ◽  
pp. 539-555 ◽  
Author(s):  
E.G. Brown ◽  
G.J. Pierce
Keyword(s):  
Prey Availability ◽  
Temporal Trends ◽  
Phoca Vitulina ◽  
Correction Factors ◽  
Fish Size ◽  
The Third ◽  
Feeding Experiments ◽  
Harbour Seals ◽  
Trawl Catches ◽  
Fish Otoliths

Scats (N=200) of harbour seals (Phoca vitulina) were collected from haul-out sites on the Island of Mousa, south-east Shetland, during July, August and September 1994. A total of 5,531 fish otoliths were identified in scats and measured to reconstruct fish lengths and weight. Gadid fishes dominated the diet of harbour seals on Mousa during the study period, both in terms of weight and the frequency with which they occurred. There was evidence for the existence of temporal trends. Over the period July–September the importance of gadids in the diet increased while that of sandeels declined. These temporal trends are probably associated with changes in prey availability. Comparisons of the size of sandeels, herring and whiting eaten by seals with trawl catches suggest that seals were probably not size-selective, but a corollary of this is that, while otolith size is reduced during passage through seal guts, application of correction factors derived from captive feeding experiments led to over-estimates of fish size.

Fatal Interspecies Mating Attempts of a Grey Seal (Halichoerus grypus) with Harbour Seals (Phoca vitulina) on the German North Sea Coast

2020 ◽  
Vol 174 ◽  
pp. 166
Author(s):  
K. Hülskötter ◽  
S. Rohner ◽  
S. Groß ◽  
J. Lakemeyer ◽  
M. Fähndrich ◽  
...  
Keyword(s):  
North Sea ◽  
Phoca Vitulina ◽  
Halichoerus Grypus ◽  
Grey Seal ◽  
Harbour Seals ◽  
Sea Coast ◽  
North Sea Coast

Histopathological findings in harbour seals (Phoca vitulina) found dead on the german north sea coast

1990 ◽  
Vol 102 (3) ◽  
pp. 299-309 ◽  
Author(s):  
U SCHUMACHER ◽  
H HORNY ◽  
G HEIDEMANN ◽  
W SCHULTZ ◽  
U WELSCH
Keyword(s):  
North Sea ◽  
Phoca Vitulina ◽  
Histopathological Findings ◽  
Harbour Seals ◽  
Sea Coast ◽  
North Sea Coast

The influence of body size and sex on the characteristics of harbour seal foraging trips

1998 ◽  
Vol 76 (6) ◽  
pp. 1044-1053 ◽  
Author(s):  
Paul M Thompson ◽  
Ann Mackay ◽  
Dominic J Tollit ◽  
Simon Enderby ◽  
Philip S Hammond
Keyword(s):  
Body Size ◽  
Activity Pattern ◽  
Diet Composition ◽  
Phoca Vitulina ◽  
Trip Duration ◽  
Energy Requirements ◽  
Endogenous Factors ◽  
Foraging Range ◽  
Harbour Seals ◽  
Size Population

Most pinnipeds disperse from centralised terrestrial sites to forage at sea, but the factors that result in variation inforaging-trip characteristics remain unclear. We investigated the influence of sex and body size on the summer foraging activityof radio-tagged harbour seals (Phoca vitulina) from Scotland. Mean foraging-trip duration (range 17–257 h) was stronglycorrelated with mean foraging range (range 4.3–55.0 km), but both were significantly shorter for females. The proportion oftime spent at sea, mean trip duration, and mean foraging range were all positively related to body size. Comparison with datafrom other study areas suggests that both environmental and endogenous factors shape foraging characteristics in this species.These sex and body size related differences in activity pattern and foraging range have important implications for themethodologies currently used to assess the population size, population energy requirements, and diet composition of coastalpinnipeds.

scholarly journals Spatial distribution and habitat preference of harbour seals (Phoca vitulina) in the Dutch North Sea

2016 ◽  
Author(s):  
Geert Aarts ◽  
◽  
Jenny Cremer ◽  
Roger Kirkwood ◽  
Jan Tjalling van der Wal ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
North Sea ◽  
Habitat Preference ◽  
Phoca Vitulina ◽  
Harbour Seals

The importance of the North Sea for winter dispersal of harbour seals Phoca vitulina from the Wadden Sea

1997 ◽  
Vol 81 (1-2) ◽  
pp. 97-102 ◽  
Author(s):  
Mardik F. Leopold ◽  
Bert van der Werf ◽  
Edith H. Ries ◽  
Peter J.H. Reijnders
Keyword(s):  
North Sea ◽  
Wadden Sea ◽  
Phoca Vitulina ◽  
The North ◽  
Harbour Seals ◽  
The North Sea

scholarly journals Relationships between in vitro lymphoproliferative responses and levels of contaminants in blood of free-ranging adult harbour seals (Phoca vitulina) from the North Sea

2013 ◽  
Vol 142-143 ◽  
pp. 210-220 ◽  
Author(s):  
Aurélie Dupont ◽  
Ursula Siebert ◽  
Adrian Covaci ◽  
Liesbeth Weijs ◽  
Gauthier Eppe ◽  
...  
Keyword(s):  
North Sea ◽  
Phoca Vitulina ◽  
The North ◽  
Harbour Seals ◽  
The North Sea ◽  
Free Ranging

Explaining diet composition of North Sea cod (Gadus morhua): prey size preference vs. prey availability

2003 ◽  
Vol 60 (2) ◽  
pp. 140-150 ◽  
Author(s):  
Jens Floeter ◽  
Axel Temming
Keyword(s):  
North Sea ◽  
Diet Composition ◽  
Gadus Morhua ◽  
Prey Size ◽  
Prey Availability ◽  
Weight Ratio ◽  
Fish Prey ◽  
Gear Efficiency ◽  
Species Specific ◽  
Size Preference

The nature and significance of size preference for fish prey in the diet selection of North Sea cod (Gadus morhua L.) was analysed. The analysis combined information on size-specific abundance derived from bottom trawl surveys with prey size frequencies in cod stomachs from the International North Sea Stomach Database. To estimate the abundance of all potential fish prey in the sea, a length-based number spectrum was calculated, corrected for gear efficiency by the application of a species-specific correction factor, and weighted by local predator abundance to take the spatial–temporal overlap between cod and its prey into consideration. A prey size preference model for cod feeding on fish is presented. Results showed that the preferred predator-to-prey weight ratio is an exponentially increasing function of predator size and an exponentially decreasing function of the slope of the number spectrum. More than 75% of fish found in the stomachs of North Sea cod originated from the least preferred quartile of the prey size range, indicating that prey abundance is the main determinant of the diet composition.

scholarly journals Predicting recurrent PDV epizootics in European harbour seals (Phoca vitulina)

2010 ◽  
Vol 8 ◽  
pp. 275 ◽  
Author(s):  
Tero Härkönen ◽  
Karin C Harding
Keyword(s):  
North Sea ◽  
Herd Immunity ◽  
Phoca Vitulina ◽  
High Rate ◽  
The North ◽  
Rate Of Spread ◽  
Phocine Distemper Virus ◽  
Harbour Seals ◽  
The North Sea ◽  
Sea Area

Phocine Distemper Virus (PDV) caused mass mortality in European harbour seals (Phoca vitulina) in 1988 and in 2002. Both epizootics likely originated from refugia in Arctic seals, where data indicate PDV hops among populations and species. The metapopulation structure of host populations is suggested to be the reason why PDV is preserved among Arctic seals, since the high rate of spread of PDV would require much larger panmictic populations to maintain an infection. The pattern of sudden outbreaks of PDVis also seen in grey seals (Halichoerus grypus), the only to date identified species that could act as a vector between Arctic and North Sea seal populations. Harbour seal populations along mainland Europe were below critical herd immunity levels by 3-5 years after the events, and thus vulnerable for new outbreaks, but historical data and the 14 years between the 2 epizootics suggest that harbour seals in the North Sea area are only rarely exposed to the infective agent. The risk for new outbreaks of the seal plague in North Sea harbour seals is likely linked to the dynamics of the disease in Arctic seal species as well asvector species.

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