The fish populations in inshore waters of the west coast of Scotland. The food and feeding of the whiting (Merlangius merlangus L,.)

The food and feeding of the whiting ( Merlangius merlangus ) of the inshore waters and sea lochs of the west of Scotland were studied from 1969–1973. Fish and Crustacea were the main food items and their occurrence in the stomachs was clearly related to the size of the whiting and also to their seasonal abundance. The diurnal changes in feeding were also investigated and the results indicated that the size of fish was again an important factor which could affect the interpretation of the seasonal data.     

Whiting migration in the Bristol Channel: a predator-prey relationship

The relationship between whiting, Merlangius merlangus (L.), and the common shrimp, Crangon crangon L., in the Bristol Channel and Severn Estuary was investigated. The whiting population was found to comprise 0-group juveniles which only remain in the region for about 10 months before moving offshore. While within the estuary, the distribution and abundance of the two species were found to be clearly related. It is hypothesized that the whiting depends on the common shrimp because it is the only abundant prey species in the winter. Both the whiting and shrimp populations were found to not follow any long-term trend in numbers. It is suggested that the whiting population is stable because it is constrained by shrimp abundance which is, in turn, limited by physical constraints. Similar predator-prey relationships may be common to many European estuaries.     

The abundance of Anisakis simplex L3 in the body-cavity and flesh of marine teleosts

Smith J. W. 1984. The abundance of Anisakis simplex L3 in the body-cavity and flesh of marine teleosts. International Journal for Parasitology14: 491–495. In experiments conducted at sea, whole (ungutted) fish of three species were stored on ice at 3–5 °C for periods from 0 to 72 h. Some Anisakis simplex L3 migrated from the body-cavity into the flesh in mackerel Scomber scombrus, but not in either blue whiting Micromesistius poutassou or whiting Merlangius merlangus. Earlier work has shown that larvae migrate into the flesh of herring Clupea harengus post mortem but not of walleye pollock Theragra chalcogramma. It seems, therefore, that larvae migrate post mortem into the flesh of ‘fatty’ species (e.g. herring, mackerel) but not of ‘non-fatty’ species (e.g. blue whiting, whiting, walleye pollock). No significant larval excapsulation occurred in isolated mackerel or whiting viscera. In vivo, most encapsulated L3 occur in the body-cavity of euphausiid-feeding fish (herring, mackerel, blue whiting, walleye pollock) but are more widely distributed throughout the tissues of piscivorous fish (whiting, cod). These observations are discussed in relation to the apparent importance of euphausiids as intermediate hosts of A. simplex.     

Trends in abundance of benthic and demersal fish populations of the lower Forth Estuary, East Scotland, from 1982–2001

The benthic and demersal fishes of the lower Forth Estuary, east Scotland, were sampled by Agassiz trawling from January 1982–December 2001. Three stations of varying distance from the mouth of the estuary were trawled at high and low water in 5 months of each year, a total of 30 trawls per annum using the same ship and net design throughout. Of 30 species collected over this period, whiting Merlangius merlangus was the most abundant, followed by eelpout Zoarces viviparus , pogge Agonus cataphractus , flounder Platichthys flesus and plaice Pleuronectes platessa . The 10 most abundant species accounted for 97·8% of the total benthic-demersal fish abundance. There was no trend in total annual species richness sampled, though total annual abundance of fishes captured decreased significantly from 1982–2001. This was largely caused by significant declines in abundance of whiting and eelpout. Fatherlasher Myoxocephalus scorpius showed a significant linear increase. None of the seven remaining most abundant species exhibited significant trends in abundance. Decline of eelpout may be attributable to increases in water temperature adversely affecting reproductive success. This is suggested by a significant negative correlation of mean annual abundance with January bottom temperature in the previous year.     

The infection dynamics and dispersion pattern of Lernaeocera branchialis L. on 0+ whiting (Merlangius merlangus L.) in the Oosterschelde (SW Netherlands)

Size and structure of the Lernaeocera branchialis population infecting 0+ whiting in the Oosterschelde were studied during 1989. Two periods of successful transmission were distinguished. The first transmission wave occurs in late spring when the post-larval whiting enter the Oosterschelde. A second wave occurs in autumn. This pattern in the infection dynamics is possibly related to seasonal variations in spatial overlap of the intermediate ( Platichthysflesus ) and the final host ( Merlangius merlangus ). The dispersion pattern of Lernaeocera branchialis within the whiting population can be described by the Poisson distribution. Possible explanations for the observed dispersion pattern are given. Evidence is presented that the rejection of pennella larvae is a key mechanism determining the abundance of L. branchialis in whiting. The potential impact of parasite-induced host mortality on population size and dispersion pattern of the parasite is discussed.     

Quantification of echinoderms (Echinodermata) on Georges Bank,and the potential influence of marine protected areas on these populations

The spatiotemporal variation of the distribution of echinoderms in the Georges Bank ecosystem was examined from 2005 to 2012. Density and abundance of representatives from echinoderm classes (brittle stars, sand dollars, sea stars, and sea urchins) were estimated using a drop camera video survey of the benthos in areas open and closed to fish trawling. The influence of closed areas on these echinoderm populations relative to a suite of key environmental and biotic factors was evaluated using Canonical Correspondence Analysis (CCA). While marine protected areas appeared to influence the distribution of sand dollars and sea stars, the distribution of brittle stars and sea urchins seemed to be defined mainly by preferred habitat conditions. According to the CCA, depth, sediment stability, temperature, predator abundance, and management area were the most important factors explaining this echinoderm assemblage. On Georges Bank, echinoderms dominate the benthic biota and are present in a variety of habitats. They can alter marine communities and are preferred prey and main predators for several commercially targeted species. The detailed information presented here (on the scale of kilometers) on abundance and spatial distribution of these populations is thus valuable towards the implementation of ecosystem‐based fisheries management.     

Predation on northern shrimp (Pandalus borealis) by three gadoid species

Northern shrimp (Pandalus borealis) is targeted by commercial fisheries, but is also an important prey in the marine food web. In this study, stomach content data were used to study predation on shrimp by three gadoid species, cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus), in six inshore areas around Iceland. The results showed that shrimp was more important in the diet of cod compared with the other two predators. However, the overall predation pressure was similar for cod and haddock due to the high abundance of haddock. Therefore, even though shrimp is not the primary source of food for haddock, this species can have a substantial effect on shrimp stocks when haddock abundance is high. In addition, while cod and haddock did not select for any particular size of shrimp, whiting seemed to preferentially target juvenile shrimp. The results suggest that due to the overall effects of these three predators on shrimp stocks, gadoids need to be included in the management of shrimp stocks as predation is one of the major drivers in the development of this important prey stock.     

Endoparasites of the blue whiting, Micromesistius poutassou from north-west Spain

The communities of metazoan endoparasites of blue whiting, Micromesistius poutassou, in waters of north-west Spain were analysed and a geographical comparison made with other localities. Four hundred blue whiting collected in July 1999 and September 2000 were examined for parasites, excluding the head and gills. Six species were found: Anisakis simplex s.l. (L3), A. physeteris (L3), Hysterothylacium aduncum (L2 and L3), Stephanostomum lophii (metacercaria), S. pristis (adult), and Prosorhynchus crucibulum (metacercaria). The latter is a new host record, and A. physeteris is reported for the first time in blue whiting from the north-east Atlantic. Host gender was not a significant predictor of abundance of any helminth species, and host length was only weakly and positively related to the abundance of A. simplex. Infracommunities were species-poor, with 56% of fish harbouring only one parasite species, and 92% up to two species. Infracommunities were strongly dominated by A. simplex (389 fish) or S. lophii (6 fish). Fish length or gender, and the year of capture, did not affect species richness nor the degree of dominance. There were no significant pair-wise associations between species. Infracommunities were basically composed of several allogenic parasites with different life histories that converge in the blue whiting through the local food web. The parasite fauna of blue whiting in the study area was poor and distinctive compared with that of other localities in the north-east North Atlantic. These peculiarities might primarily be related to the composition of the local community of definitive hosts, although there might also be some influence of the geographical distribution of parasites.     

Unchanging diet in a stable colony: contemporary and past diet composition of black-legged kittiwakes <Emphasis Type="Italic">Rissa tridactyla</Emphasis> at Helgoland,south-eastern North Sea

In contrast to the situation at the west coast of the North Sea, the breeding colony of black-legged kittiwakes Rissa tridactyla at Helgoland in the south-eastern North Sea did not exhibit severe declines since 1990 but instead numbers increased and only lately stabilised. Declines at the west coast of the North Sea were attributed to a lower abundance and lower quality of the key prey, sandeels. We hypothesised that kittiwakes at Helgoland do not rely as heavily on sandeels as their conspecifics. We analysed stomach contents of nestlings and adults of 2001, 2002, 2004 and 2006. In concordance with earlier studies of the 1980s and 1990s, young whiting Merlangius merlangus was the most important prey species in 2001, 2002 and 2004. Clupeids and sandeels were consumed in lower proportions. While earlier studies suggested whiting to originate from fisheries discards, evidence now supports that kittiwakes prey upon whiting in areas of hydrographic fronts. No whiting was recovered in samples of 2006 and the proportion of fish prey was low. Main prey items were polychaete worms (Nereidae), which were presumably consumed as swarming Heteronereis stages. An observed strong rise in water temperature in summer 2006 might have influenced food availability of kittiwakes by inducing swarming of Nereidae. Overall, kittiwakes breeding on Helgoland showed a positive population trend for several decades while mainly feeding on whiting.     

Changes in the parasite fauna of whiting Odontogadus merlangus L. with age and sex of host, season, and from different areas in the vicinity of the Isle of Man

Infestation of whiting with the helminths Derogenes varicus Müller, Hemiurus communis Odhner, Grillotia erinaceus Van Beneden (plerocercoids) and Contracaecum clavatum Rudolphi, and the copepod Lernaeocera branchialis L., increased with the age of the fish but infestation with the helminths Lecithaster gibbosus Rudolphi, Stephanostomum pristis Looss and Podocotyleatomon and the copepod Clavella uncinata Müller decreased as the fish aged. Infestation with the gill monogenean Diclidophora merlangi Kuhn remained at much the same level in fish 1–5+ years old. Derogenes, Hemiurus, Lecithaster, Cotracaecum and Stephanostomum showed seasonal fluctuations in the levels of their populations in whiting. In all cases the parasites reached a main peak in the summer and early autumn, a time when juvenile digeneans were most apparent.
Whiting from Morecambe Bay were less infested with Clavella than whiting taken from other areas. Experimental evidence suggests that the lower salinity of Morecambe Bay may be responsible; however, this could not account for the lower infestation of Morecambe Bay whiting by Diclidophora which appeared to be unaffected by a lowered salinity. Whiting from the east side of the Isle of Man were more infested with Lernaeocera but less infested with Diclidophora than fish from the west side of the island. The myxosporidian Myxobolus aeglefini Auerbach was externally visible in the sclera of whiting from the east side of the island but absent from the sclera of whiting from the west side of the island. It is, therefore, suggested that whiting to the east of the Isle of Man form a separate sub-stock from those to the west of the island.     

The diet of blue whiting, hake, horse mackerel and mackerel off Portugal

This paper deals with the diets of blue whiting Micromesistius poutassou (Risso 1810), hake Merluccius merluccius (L. 1758), horse mackerel Trachurus trachurus (L. 1758), and mackerel Scomber scombrus (L. 1758) off Portugal and explores variations in fish length, water depth, latitude and season. All four species feed on fish; however, hake and mackerel are the first and second most important predators, respectively, blue whiting being the most important fish prey for both species. The diets of blue whiting and horse mackerel are composed mainly of crustaceans. Diet variations according to predator fish size are more important than either latitude or depth. In the diets of blue whiting, hake and horse mackerel, prey importance increases with predator size. For blue whiting and horse mackerel, diet variations with fish length and water depth are correlated: small fish are closely associated with coastal areas where they feed on copepods and decapod larvae. Seasonality in the diet is apparent for blue whiting, hake and mackerel. For blue whiting, the decapod Pasiphaea sivado is the most important prey in summer and autumn, being replaced by the euphausid Meganyctiphanes norvegica in winter. In the diet of hake, seasonality was characterised by the major importance of Macroramphosus scolopax in autumn, whereas the diet of mackerel consisted of zooplankton in summer, fish and decapods in autumn and decapod larvae in winter. Seasonal changes in the diet of horse mackerel correspond to a higher diversity of prey in autumn compared to other seasons (although euphausids are the main prey in all seasons). Seasonality in feeding activity is not as marked for the other species as it is for horse mackerel; the percentage of empty stomachs of horse mackerel is greatest in winter, when spawning takes place at the Portuguese coast.     

Spatial and temporal distribution of whiting (Sillaginidae) in Moreton Bay, Queensland

Five species of whiting (Sillaginidae) inhabit Moreton Bay. The school whiting, Sillago bassensis , and stout whiting, S. robusta , are rare, caught occasionally by trawlers in areas of sandy substrates. The sand whiting, S. ciliata , golden-lined whiting, S. analis , and trumpeter whiting, S. maculata , are very common throughout the year. Sillago maculata is distributed almost throughout Moreton Bay, from 1 to 30 m depth. Sillago ciliata and S. analis are shallow water dwellers, from the shoreline to 3 m and 5 m depth, respectively. In the shallow waters, S. ciliata prefers the sandy substrates and S. analis the mud-sandy substrates. Distributions related to the depth, habitat preference, juvenile-adult grounds, food availability, interspecific competition, and winter season are discussed.     

Climate oscillation and the invasion of alien species influence the oceanic distribution of seabirds

Spatial and temporal distribution of seabird transiting and foraging at sea is an important consideration for marine conservation planning. Using at‐sea observations of seabirds (n = 317), collected during the breeding season from 2012 to 2016, we built boosted regression tree (BRT) models to identify relationships between numerically dominant seabird species (red‐footed booby, brown noddy, white tern, and wedge‐tailed shearwater), geomorphology, oceanographic variability, and climate oscillation in the Chagos Archipelago. We documented positive relationships between red‐footed booby and wedge‐tailed shearwater abundance with the strength in the Indian Ocean Dipole, as represented by the Dipole Mode Index (6.7% and 23.7% contribution, respectively). The abundance of red‐footed boobies, brown noddies, and white terns declined abruptly with greater distance to island (17.6%, 34.1%, and 41.1% contribution, respectively). We further quantified the effects of proximity to rat‐free and rat‐invaded islands on seabird distribution at sea and identified breaking point distribution thresholds. We detected areas of increased abundance at sea and habitat use‐age under a scenario where rats are eradicated from invaded nearby islands and recolonized by seabirds. Following rat eradication, abundance at sea of red‐footed booby, brown noddy, and white terns increased by 14%, 17%, and 3%, respectively, with no important increase detected for shearwaters. Our results have implication for seabird conservation and island restoration. Climate oscillations may cause shifts in seabird distribution, possibly through changes in regional productivity and prey distribution. Invasive species eradications and subsequent island recolonization can lead to greater access for seabirds to areas at sea, due to increased foraging or transiting through, potentially leading to distribution gains and increased competition. Our approach predicting distribution after successful eradications enables anticipatory threat mitigation in these areas, minimizing competition between colonies and thereby maximizing the risk of success and the conservation impact of eradication programs.     

The winter abundance and distribution of birds in western peter the Great Bay in the Sea of Japan

The data on the abundance and distribution of sea birds and waterfowl at the coast of southern Primorye and distribution diagrams of the sea ducks along the surveyed coast in winter season are given. The dependence of the presence of the birds in certain coastal areas on the winter ice condition was revealed.     

Potential changes to the biology and challenges to the management of invasive sea lamprey Petromyzon marinus in the Laurentian Great Lakes due to climate change

Control programs are implemented to mitigate the damage caused by invasive species worldwide. In the highly invaded Great Lakes, the climate is expected to become warmer with more extreme weather and variable precipitation, resulting in shorter iced‐over periods and variable tributary flows as well as changes to pH and river hydrology and hydrogeomorphology. We review how climate change influences physiology, behavior, and demography of a damaging invasive species, sea lamprey (Petromyzon marinus), in the Great Lakes, and the consequences for sea lamprey control efforts. Sea lamprey control relies on surveys to monitor abundance of larval sea lamprey in Great Lakes tributaries. The abundance of parasitic, juvenile sea lampreys in the lakes is calculated by surveying wounding rates on lake trout (Salvelinus namaycush), and trap surveys are used to enumerate adult spawning runs. Chemical control using lampricides (i.e., lamprey pesticides) to target larval sea lamprey and barriers to prevent adult lamprey from reaching spawning grounds are the most important tools used for sea lamprey population control. We describe how climate change could affect larval survival in rivers, growth and maturation in lakes, phenology and the spawning migration as adults return to rivers, and the overall abundance and distribution of sea lamprey in the Great Lakes. Our review suggests that Great Lakes sea lamprey may benefit from climate change with longer growing seasons, more rapid growth, and greater access to spawning habitat, but uncertainties remain about the future availability and suitability of larval habitats. Consideration of the biology of invasive species and adaptation of the timing, intensity, and frequency of control efforts is critical to the management of biological invasions in a changing world, such as sea lamprey in the Great Lakes.     

Sea warming and fish distribution: the case of the small pelagic fish, Sardinella aurita, in the western Mediterranean

This study analyses the temporal and spatial changes in abundance and distribution of the warm water species round sardinella (Sardinella aurita) in the western Mediterranean over the last decades in relation to sea water temperature. In the western Mediterranean basin (1950–2003), a significant positive relationship was found between round sardinella landings and temperature anomalies. Along a latitudinal gradient off the Mediterranean Iberian coast (1989–2004), a gradual increase in species abundance was observed from south to north, with a certain time lag going northwards, associated with the increase in sea water temperature. The abundance of round sardinella in the two warmest and southernmost areas was positively and significantly correlated with sea surface temperature registered during the start of gonad maturation the previous year. In addition, the positive relationship established between water temperature and abundance of round sardinella in the coldest and northernmost study area demonstrates that there is a temperature limit for the distribution of this species in the western Mediterranean. In addition, this study analyses round sardinella larvae distribution and abundance in the summers of 2003 and 2004, and conducts a comparison with the situation 20 years ago (summer 1983). Results show a marked increase in larval abundance during the last decades and the present appearance of larvae in the northernmost study areas, where they did not occur 20 years ago. This indicates the successful reproduction of round sardinella in the northern part of the Mediterranean, where the species has expanded, confirming its establishment in the area.     

Notes on helminth parasites of the whiting Odontogadus m. merlangus (L.) from the northern Irish Sea

In an examination of 1352 whiting from the Irish Sea 13 helminth species were discovered. One species, Scolex polymorphus Rudolphi, was a new species associated with whiting and 7 other species were new species for whiting from the Northern Irish Sea. The species of the digenean genus Podocotyle found in whiting is probably an ecotype of P. atomon. It was concluded that the bothridial structure of 5. polymorphus cannot be used for diagnostic purposes nor to determine early and late stages of the larvae. The number of Diclidophora merlangi Kuhn (Monogenea) from each monthly sample with eggs in the uterus is directly proportional to temperature, but egg production under experimental conditions was greatest at 6° C. Several theories are proposed to explain these apparently contradictory observations. The life-history of the digenean Stephanostomum pristis Looss, appears to be unusual in that the 2nd intermediate host may be planktonic. The nematode Contra caecum clavatum Rudolphi is found both as larvae and adults but larvae comprise the greater part of the worm population. The discovery of small stage II larvae in the stomach of whiting supports the theory that only one intermediate host is necessary for the development of Contmcaecum . There were significantly more female C. clavatum than male but a 1: 1 sex ratio is demonstrated by the acanthocephalan Echinorhynchus gadi Muller. Early and late forms of the plerocercoid of Grillotia erinaceus Van Beneden are identified. The early form occurred predominantly in the young whiting.     

The reproductive biology of poor-cod, Trisoptems minutus L., whiting, Merlangius merlangus L., and Norway pout, Trisoptems esmarkii Nilsson, off the west coast of Scotland

The reproductive biology of poor-cod, Trisoptems minutus L., whiting, Merlangius merlangus L., and Norway pout, Trisoptems esmarkii Nilsson, was studied in western Scottish waters. Sex ratios, size and age at maturation and spawning seasons were determined and compared with other areas. The large juvenile stocks found in inshore areas at the western entrance of the Great Glen were derived from spawning grounds west of Mull, in poor-Cod. In whiting and Norway pout the location of spawning grounds was inferred from the occurrence of planktonic larvae and postlarvae and the hydrography of the area.     

MOVEMENTS, HOME RANGE, AND TERRITORIES OF MALE SEA OTTERS OFF CENTRAL CALIFORNIA

Sixty male sea otters ( Enhydra lutris ) were tagged on the rear flippers with colored tags. Of these, 46 (77%) were resighted. Movements of 127 km were documented for adults and 187 km for subadults. Adults maintained breeding territories that averaged 40.3 ha ( n = 10, SE = 4.0). They returned to the same territory seasonally for up to seven consecutive years. Territorial males moved from areas of high male abundance to areas of high female abundance on a seasonal basis. During the winter, 74% of adult males left breeding areas and joined concentrations of males located near the ends of the range. Thirty percent of the subadult males were observed in male groups near the extremities of the range. During the summer and fall, the density of adult males (15/1,000 ha) and adult male to independent otter (non-pup) ratio (1:5) in female areas was highest. The number of adult males in areas of female abundance was inversely related to the number of dependent pups, perhaps because when pup numbers are low (late summer and fall) the number of estrous females is high. Subadult males may remain in female areas on a year round basis until their second or third year. However, they were not generally associated with adult females.     

The rotifer fauna of peat-swamps in southern Thailand

Different taxa have had different degrees of success in invading and proliferating in the deep sea. The reasons for these differences are not well known, and exemplars need to be studied to provide insight as to factors that lead to success in the deep sea. Because the abundance of the deep-sea fauna taken as a whole declines with depth, the absolute abundance of a taxon is not an appropriate metric of its success. Rather, a taxon whose abundance declines as rapidly as or less rapidly than the general trend should be considered successful. In this paper, I used the macrofauna to define the general trend of abundance change with depth. When I compared the trend of abundance of harpacticoids to that for macrofauna, I found that harpacticoid abundance decreased less rapidly. Thus, harpacticoids are unusually successful in the deep sea. The reasons for their success are unknown, but I discuss three possible explanations.