Growth and maturation of roker Raja clavata L. in the Solway Firth

Two hundred and seventy-one Raja clavata taken by otter trawl from the Solway Firth were examined for size, sex and state of maturity. Size relationships for both sexes were similar. Total length and disc width were linearly related as were disc width with wing width. Males and females appear to mature at 42 and 45 cm disc width respectively. The Solway population is heavily exploited by an unrestricted commercial fishery and a considerable proportion (48·6%) of the presently retained catch is immature. It is suggested that fishing pressure has brought about a reduction in the size at which female fish mature.     

Ecology of Allis Shad Alosa alosa and Twaite Shad Alosa fallax in the Solway Firth, Scotland

The basis of this study were 132 adult Allis Shad and 150 Twaite Shad collected as bycatches from salmon stake nets in Scotland on the north side of the Solway Firth. Most (60%) of the Allis Shad were immature fish 2–3 years of age (mean length 305 mm). Mature males were younger (3–5 years) and smaller (mean length 421 mm) than females (4–6 years and 481 mm mean length). The largest Allis Shad was a female of 515 mm and 2183 g. In contrast, almost all the Twaite Shad were mature, the males younger (3–5 years) and smaller (mean length 341 mm) than the females (4–6 years and 364 mm mean length). The largest Twaite Shad was a female of 400 mm and 1213 g. The food of Allis Shad consisted mainly of small zooplankton with some fish and larger Crustacea. Fine vegetable fragments were common in the stomachs and attributed to filter feeding. The food of Twaite Shad was mainly small fish with some Crustacea. Mature Allis Shad of both sexes with large gonads (maximum female GSI: 20.63) were found throughout the spring and summer but no definite evidence of local spawning was obtained. Mature Twaite Shad of both sexes with large gonads (maximum female GSI: 23.32) were found until early July, thereafter most of the fish were spent. It appears that Twaite Shad spawn locally in June. Some hybrids between the two species were found.     

The occurrence and performance of leucistic Barnacle Geese Branta leucopsis

The paper reports the occurrence of whitish 'leucistic' forms in populations of Barnacle Geese Branta leucopsis. A total of 15 (including 11 in the last 21 years) have been reported in the population breeding in Svalbard and wintering in the Solway Firth, northern Britain, whereas the two other populations, though much larger, have produced only one bird of the same type between them in the last 30 years. Leucism is controlled by a single, recessive allele.
The median lifespan of leucistic birds is 2–3 years, compared to 8–10 years for normal plumaged birds. This is because they are sought out by (illegal) hunters. There is no evidence that there is any difference in pairing or breeding performance between white and normal birds, though one male, which is still alive aged 18 years, has produced 13 young; this performance is matched fay less than 2% of normal geese.
It is suggested that the Svalbard population was established recently, from a few founders from the Siberian population; if one or two of these carried the allele controlling leucism, this would explain its much higher prevalence in this population than in the other discrete groups of Barnacle Geese.     

The origins of Atlantic salmon (Salmo salar L.) recolonizing the River Mersey in northwest England

By the 1950s, pollution had extirpated Atlantic salmon in the river Mersey in northwest England. During the 1970s, an extensive restoration program began and in 2001, an adult salmon was caught ascending the river. Subsequently, a fish trap was installed and additional adults are now routinely sampled. In this study, we have genotyped 138 adults and one juvenile salmon at 14 microsatellite loci from across this time period (2001–2011). We have used assignment analysis with a recently compiled pan‐European microsatellite baseline to identify their most probable region of origin. Fish entering the Mersey appear to originate from multiple sources, with the greatest proportion (45–60%, dependent on methodology) assigning to rivers in the geographical region just north of the Mersey, which includes Northwest England and the Solway Firth. Substantial numbers also appear to originate from rivers in western Scotland, and from rivers in Wales and Southwest England; nonetheless, the number of fish originating from proximal rivers to the west of the Mersey was lower than expected. Our results suggest that the majority of salmon sampled in the Mersey are straying in a southerly direction, in accordance with the predominantly clockwise gyre present in the eastern Irish Sea. Our findings highlight the complementary roles of improving water quality and in‐river navigability in restoring salmon to a river and underlines further the potential benefits of restoration over stocking as a long‐term solution to declining fish stocks.     

Redescription of Alcyonidium my till Dalyell, 1848 (Bryozoa: Gtenostomatida)

Reproduction in the ctenostomate bryozoan Alcyonidium mytili Dalyell, 1848, was studied over 2 years, revealing confusion in the literature over the diagnostic characters of the species and incorrect assumptions about the mode of reproduction. The literature is briefly reviewed and an approximate type locality from the Firth of Forth, Scotland, is identified. Alcyonidium mytili is comprehensively redescribed from material collected in the Firth of Forth and from 2 years' collections in the Daugleddau estuary, near Pembroke Dock, South Wales. Zooid and polypide dimensions and modal tentacle number (16) have been determined from large samples. Most importantly A. mytili possesses a conspicuous intertentacular organ when reproductive; is oviparous, with eggs discharged through the intertentacular organ developing into cyphonautes larvae; and has a prolonged winter reproductive period. The contrary indications in the literature are a consequence of confusion with a superficially similar but larviparous species.     

Changes in species diversity and size composition in the Firth of Clyde demersal fish community (1927-2009)

Following the repeal in 1962 of a long-standing ban on trawling, yields of demersal fish from the Firth of Clyde, southwest Scotland, increased to a maximum in 1973 and then declined until the directed fishery effectively ceased in the early 2000s. Since then, the only landings of demersal fish from the Firth have been by-catch in the Norway lobster fishery. We analysed changes in biomass density, species diversity and length structure of the demersal fish community between 1927 and 2009 from scientific trawl surveys, and related these to the fishery harvesting rate. As yields collapsed, the community transformed from a state in which biomass was distributed across numerous species (high species evenness) and large maximum length taxa were common, to one in which 90 per cent of the biomass was vested in one species (whiting), and both large individuals and large maximum length species were rare. Species evenness recovered quickly once the directed fishery ceased, but 10 years later, the community was still deficient in large individuals. The changes partly reflected events at a larger regional scale but were more extreme. The lag in response with respect to fishing has implications for attempts at managing a restoration of the ecosystem.     

Functional relationship between sealworm (Pseudoterranova decipiens, Nematoda, Ascaridoidea) burden and host size in Atlantic cod (Gadus morhua).

A model is proposed to describe the accumulation of sealworm parasites (Pseudoterranova decipiens, Nematoda, Ascaridoidae) in Atlantic cod (Gadus morhua). The model predicts the total amount of food eaten by a fish to reach its size. In young fish growth is linear in time and average parasite burdens are predicted to increase with the cube of the average length of the fish divided by its growth rate. An analysis of worm burdens in cod caught by the commercial fishery in the Firth of Clyde (Strathclyde, Scotland) between 1964 and 1970 illustrates how average parasite abundances at age, length, or fixed time of the year can be compared. It is concluded that exposure did not vary significantly over these years. Extensive apparent inter-annual variations in worm burdens of cod newly recruited to the fishery are well explained by differences in the age composition of cod catches.     

The biology of Fries' goby, Lesueurigobius friesii (Malm), in the Firth of Clyde, Scotland, and a comparison with other stocks

The general biology of a population of Lesueurigobius friesii in the Firth of Clyde, Scotland, was studied between October 1977 and December 1979. In this population the fish attained 95 mm and lived a maximum of nine years. The population growth characteristics from von Bertalanffy growth curves showed that the Clyde stock of L. friesii attained a greater maximum theoretical length (L∞) than stocks in the Lynn of Lorne or Biscay and had a lower growth coefficient ( K ). In all three stocks, the majority of the growth in length ( A _0.95) was achieved by the end of the fourth year of life. In general the sex ratio was 1: 1 throughout the season. Spawning occurred from May to August, approximately the same time as the Lynn of Lorne stock. Sexual maturity was first reached at a smaller size in males than females. The abundance of L. friesii in the Clyde fluctuated considerably with reduced numbers of fish caught just after spawning.     

Temporal variations in the skin of Atlantic salmon Salmo solar L.

The thickness of the skin of Atlantic salmon increases throughout the first two years of life. This increase involves, principally, an increase in the connective tissue of the dermis, and occurs independently of sexual maturity. The concentration of mucous cells in the epidermis changes seasonally, being least during the winter period. No sexual dimorphism is observed in these features among sexually immature fish. The epidermis of precociously mature male parr is thicker and contains more mucous cells than that of sexually immature individuals.     

Variation in dog-whelk shells in relation to wave action and crab predation

In Nucella lapillus there is usually a progressive gradation in mean shell shape from short squat individuals on exposed headlands to more elongated ones in shelter. This pattern has been attributed to the differential selective effects of wave action and crab predation, although it would almost certainly be an oversimplification to imagine these as the only significant forces involved, especially near the limits of the species' distribution.
However, whilst this pattern of shell-shape variation with exposure is generally true over most of the animal's range in both Europe and North America, there are exceptions. There are occasional enclaves with much more elongated shells than would normally have been expected. Sometimes these are so abundant, as in the Severn Estuary, that all dog-whelk enclaves are unusually elongated, regardless of the exposure of their habitat.
In other areas, such as south-eastern England, the Solway Firth and the area around the mouth of the Conway the shells are not unusually elongated, but the enclaves show very little variation: a normal sheltered-shore form is seen wherever the species occurs. Shetland samples appear to be a combination of this pattern (predominating) with the 'normal' one showing the full range of shellshape variation.
Nucella appears in the Atlantic fossil record at the end of the Pliocene without any antecedent forms. It is assumed to have colonized from the Pacific and exploited the vacant niche before the onset of the Ice Age. Successive advances and retreats of the ice, with attendant changes in sea level, will have served to break up and recombine those dog-whelk populations that were not eliminated. It is postulated that the modern Nucella lapillus is a combination of several genetically distinct populations, some of which show the full range of variation and may respond to the selective effects of crabs and waves, and some of which do not and show little variation.     

Ecological Meltdown in the Firth of Clyde,Scotland: Two Centuries of Change in a Coastal Marine Ecosystem

Background

The Firth of Clyde is a large inlet of the sea that extends over 100 km into Scotland''s west coast.

Methods

We compiled detailed fisheries landings data for this area and combined them with historical accounts to build a picture of change due to fishing activity over the last 200 years.

Findings

In the early 19^th century, prior to the onset of industrial fishing, the Firth of Clyde supported diverse and productive fisheries for species such as herring (Clupea harengus, Clupeidae), cod (Gadus morhua, Gadidae), haddock (Melanogrammus aeglefinus, Gadidae), turbot (Psetta maxima, Scophthalmidae) and flounder (Platichthys flesus, Pleuronectidae). The 19^th century saw increased demand for fish, which encouraged more indiscriminate methods of fishing such as bottom trawling. During the 1880s, fish landings began to decline, and upon the recommendation of local fishers and scientists, the Firth of Clyde was closed to large trawling vessels in 1889. This closure remained in place until 1962 when bottom trawling for Norway lobster (Nephrops norvegicus, Nephropidae) was approved in areas more than three nautical miles from the coast. During the 1960s and 1970s, landings of bottomfish increased as trawling intensified. The trawl closure within three nautical miles of the coast was repealed in 1984 under pressure from the industry. Thereafter, bottomfish landings went into terminal decline, with all species collapsing to zero or near zero landings by the early 21^st century. Herring fisheries collapsed in the 1970s as more efficient mid-water trawls and fish finders were introduced, while a fishery for mid-water saithe (Pollachius virens, Gadidae) underwent a boom and bust shortly after discovery in the late 1960s. The only commercial fisheries that remain today are for Nephrops and scallops (Pecten maximus, Pectinidae).

Significance

The Firth of Clyde is a marine ecosystem nearing the endpoint of overfishing, a time when no species remain that are capable of sustaining commercial catches. The evidence suggests that trawl closures helped maintain productive fisheries through the mid-20^th century, and their reopening precipitated collapse of bottomfish stocks. We argue that continued intensive bottom trawling for Nephrops with fine mesh nets will prevent the recovery of other species. This once diverse and highly productive environment will only be restored if trawl closures or other protected areas are re-introduced. The Firth of Clyde represents at a small scale a process that is occurring ocean-wide today, and its experience serves as a warning to others.     

Impact of fish predation on cladoceran body weight distribution and zooplankton grazing in lakes during winter

1. It is well accepted that fish, if abundant, can have a major impact on the zooplankton community structure during summer, which, particularly in eutrophic lakes, may cascade to phytoplankton and ultimately influence water clarity. Fish predation affects mean size of cladocerans and the zooplankton grazing pressure on phytoplankton. Little is, however, known about the role of fish during winter. 2. We analysed data from 34 lakes studied for 8–9 years divided into three seasons: summer, autumn/spring and winter, and four lake classes: all lakes, shallow lakes without submerged plants, shallow lakes with submerged plants and deep lakes. We recorded how body weight of Daphnia and then cladocerans varied among the three seasons. For all lake types there was a significant positive correlation in the mean body weight of Daphnia and all cladocerans between the different seasons, and only in lakes with macrophytes did the slope differ significantly from one (winter versus summer for Daphnia). 3. These results suggest that the fish predation pressure during autumn/spring and winter is as high as during summer, and maybe even higher during winter in macrophyte‐rich lakes. It could be argued that the winter zooplankton community structure resembles that of the summer community because of low specimen turnover during winter mediated by low fecundity, which, in turn, reflects food shortage, low temperatures and low winter hatching from resting eggs. However, we found frequent major changes in mean body weight of Daphnia and cladocerans in three fish‐biomanipulated lakes during the winter season. 4. The seasonal pattern of zooplankton : phytoplankton biomass ratio showed no correlation between summer and winter for shallow lakes with abundant vegetation or for deep lakes. For the shallow lakes, the ratio was substantially higher during summer than in winter and autumn/spring, suggesting a higher zooplankton grazing potential during summer, while the ratio was often higher in winter in deep lakes. Direct and indirect effects of macrophytes, and internal P loading and mixing, all varying over the season, might weaken the fish signal on this ratio. 5. Overall, our data indicate that release of fish predation may have strong cascading effects on zooplankton grazing on phytoplankton and water clarity in temperate, coastal situated eutrophic lakes, not only during summer but also during winter.     

The movements of brown trout, Salmo trutta (L.) in Loch Leven, Kinross, Scotland

Juvenile trout enter Loch Leven during autumn and winter from the nursery streams, spend their adolescent phase offshore until reaching a length of 0.30 cm, and then move to the littoral areas in early summer. There are two types of littoral area:'favourable'areas from which movement of individual fish in the summer is very restricted, and'unfavourable'areas used briefly in early summer from which movement away is pronounced. Trout are absent from the littoral areas in winter. In subsequent summers homing to previous feeding areas is characteristic of fish from'favourable'areas, with a tendency for older fish to move to the south east area of the loch. Spawning runs occur simultaneously into the main inflows, chiefly between October and December. Emigration into the outflow occurs, but is probably unimportant.     

Year-to-year variation in larval fish assemblages of the Southern North Sea

In order to test the temporal stability within and the reproducibility of larval fish assemblages between years, the larval fish assemblage at Helgoland Roads, North Sea (NE Atlantic) was quantitatively sampled almost daily from January 2003 to December 2005. The survey resulted in a total of 462 samples containing 50,632 larval fish of at least 42 taxa. In winter the larval fish assemblage was mainly dominated by larvae emerging from demersal eggs. This changed gradually to larvae hatching from pelagic eggs. Larvae from pelagic eggs dominated the ichthyoplankton assemblage in summer. A remarkably stable seasonality in terms of dominance patterns with recurring, season-specific fish assemblages was observed over the 3 years, despite substantial variation in environmental conditions such as a temperature difference of almost 20°C between summer and winter. The lesser sandeel (Ammodytes marinus), was the only species which showed significant fluctuations in abundance between the years. After removal of this species from the analysis, the dominance patterns of the remaining fish species were almost identical between years.     

Lymphocytopenia and the overwinter survival of Atlantic salmon parr, Salmo salar L.

The overwinter mortality rate of underyearling S2 Atlantic salmon parr (fish that will remain in fresh water for at least two years prior to smoltification) was almost ten times greater than that of S1 parr (fish that will smoltify after 1 year in fresh water) kept under similar conditions. The loss of condition ( K factor) of the S2 parr was proportionally greater than that of S1 parr during the early winter months and this coincided with a marked lymphocytopenia and thrombocytopenia in the S2 parr. Limited evidence indicates that S2 parr have chronically elevated blood cortisol levels during the winter months. It is suggested that chronic stress resulting (in part) from nutritional deficiency has a debilitating effect on the defence systems of these fish. The ultimate cause of mortality in most cases was bacterial fin-rot and/or fungal ( Saprolegnia ) infection. These findings are discussed in relation to the habitat requirements of overwintering salmonid fish.     

Infestations of wild adult Atlantic salmon (Salmo salar L.) by the ectoparasitic copepod sea louse Lepeophtheirus salmonis Krøyer: prevalence,intensity and the spatial distribution of males and [2pt] females on the host fish

The copepod Lepeophtheirus salmonis Krøyer is a specific ectoparasite of North Atlantic and Pacific salmonids in their marine phases. We compared infestations of L. salmonis on wild Atlantic salmon (Salmo salarL.) captured in estuarine (Firth of Tay, east Scotland; 1995, 1996) and marine coastal waters (Strathy Point, north Scotland; 1998, 1999). Host fish from the Tay were caught by sweep netting, whilst those from Strathy Point were trapped in anchored bagnets. Fish capture method and exposure of the parasites to brackish conditions may both have detrimental effects on the retention of L. salmonis by the host, and hence possibly lead to their being under-estimated on returning adult fish. At Strathy Point, we recorded (i) an infestation prevalence of 100%, (ii) mean log abundances of pre-adult + adult L. salmonis at 19 (1998) and 24 (1999) per fish, (iii) 85/93% of all L. salmonis as being adults and (iv) overall 68/69% females. Fish caught in the upper Firth of Tay showed significantly lower prevalences, intensities and abundances of L. salmonis and probably had lost part or all of their lice burdens prior to capture, whereas those sampled from Strathy Point were apparently minimally affected by capture method or brackish water influences. The loss of parasites for the Tay fish was not markedly biased to males or females, or to pre-adult versus adult developmental stages. There were significantly greater abundances of L. salmonis on two sea-winter fish (30 lice per fish) than on one sea-winter fish (17 lice per fish) sampled at Strathy Point in 1998. There are several possible explanations for such age-related patterns of abundance, but the indications are that (i) initial infestation of smolts occurs in coastal waters, (ii) infestation of hosts in the open ocean is a persistent event, and (iii) oceanic reinfestation outweighs mortality losses of L. salmonis. This parasite typically occupies rather few zones on the host fish covering only a small percentage of the total available body surface area. Female predominance appears to be characteristic of L. salmonisinfestations of wild Atlantic salmon; this is in marked contrast to reports of extreme male dominance on farmed stocks. Adult females predominated on the epidermis adjacent to, and posterior of, the insertion of the anal fin and along the posterior dorsal midline between the dorsal and caudal fins. Males predominated on the sides of the head and along the dorsal midline between the head and the dorsal fin. Mate guarding/precopulatory pairs are formed between pre-adult II females and adult males. The significant correlation between the distribution of pre-adult females and adult males may be indicative of pre-adult females actively seeking out adult males, but more likely is due to the (large) adult females competitively ousting all smaller life stages (female and male) from those preferred zones. Given the relatively low fecundity of adult females, and observations of 100% prevalence of L. salmonis, the infective planktonic copepodid stage evidently is extremely efficient at locating and establishing upon its host fish in the pelagic environment.     

New data on biology of the pearlfish <Emphasis Type="Italic">Maurolicus imperatorius</Emphasis> (Sternopthychidae) from the Emperor Seamount Chain

The pearlfish Maurolicus imperatorius occurs above seamounts of the Emperor Seamount Chain between 30°–40° N and 168°–176° E. It forms dense aggregations at the daytime in the upper mesopelagial above the ground and disperses in the dark period of the day in the surficial layer. Judged by maturation dynamics of gonads, the spawning of this species occurs from January until April with the maximum in March. Catches of this species are characterized by expressed seasonal dynamics of size composition. Juveniles appear in catches in the end of spring-the beginning of summer. The maximum recorded SL is 68 mm. Among large fish, females dominate. The part of females is maximum in winter and minimum in spring. The age of fish with AC 46–63 mm is 265–420 days. The growth rate is abruptly retarded at the fourth month of life when the length 40–45 mm is attained. Life duration of most fish does not exceed 1.5 years, though some specimens may attain the age of two years. It is supposed that the presence of another species—M. japonicus—on the Emperor Seamount Chain may result from passive transfer in the Kuroshio waters.     

Onset of maturity and cohort composition at spawning of Baltic sprat Sprattus sprattus on the basis of otolith macrostructure analysis

Data on catch per unit effort (CPUE) from the Danish commercial fishery showed dense aggregations of sprat Sprattus sprattus born in 1997 in the main spawning area of the Baltic Sea during May 1999. After the analysis of their otolith macrostructure, these fish were found to have a shorter distance to the beginning of the first winter zone compared to fish from the same cohort caught in other months. At the same time, the number of fish with large otoliths at the period of winter zone formation tended to decrease or even disappear. The otolith size at winter zone formation ( O _W) was found to be a good predictor of sprat total length ( L _T) and mass ( M ) in age group 0 years. Changes in the otolith size distribution over time were related to variations in cohort composition depending on the L _T and M attained during the juvenile stage. Examination of the gonads suggested two life history patterns: 1) individuals achieving a larger L _T and M during the first growing season may contribute at age 1 years to the spawning stock and the fishery, whereas 2) individuals attaining smaller L _T and M contribute in larger amounts to both the spawning stock and the fishery later, when they are at age 2 years. Moreover, changes in the relationship between O _W and L _T and M were related to differences in growth trajectories for sprat born during the same spawning season. Smaller sprat as group 0 years continued growing during the second growing season delaying maturity compared to larger individuals from the same cohort.     

Growth, movements and diet of the terapontid Amniataba caudavittata in an Australian estuary

Samples of Amniataba caudavittata were collected from the Swan Estuary in south-western Australia between February 1977 and December 1980, using seine nets in inshore shallow waters and gillnets and otter trawls in offshore waters. Although fish could only be aged using otoliths until they were 18–22 months old, they had by that time reached c . 75% of their final length. The mean lengths of the cohorts determined by using MIX, which analysed each of the monthly length-frequency distributions independently, were similar to those yielded by MULTIFAN, which constrains the means of each of the sequential and corresponding cohorts to a von Bertalanffy growth curve. Consequently, the von Bertalanffy growth curve parameters determined by MULTIFAN and those derived from the use of the means produced by MIX were similar. The clear cut trends exhibited by the progression of modal lengths in successive samples, and their close correspondence to the trends shown by the growth curves, demonstrate that many A. caudavittata live for at least 3 years. Growth was seasonal and confined to the warmer months of the year. The apparent negative growth recorded in winter can be attributed to a tendency for the smaller representatives of the different cohorts to remain inshore at that time and thus to be more susceptible to capture by seine netting, the main sampling method. Offshore movements by larger fish in the winter allow those fish to remain in the high salinities found beneath the pronounced haioclines that form in the deeper waters of this estuary during the heavy freshwater discharge that occurs typically at that time of the year. Adult A. caudavittata move into the upper estuary where spawning occurs, with considerable numbers of the resultant juveniles then moving downstream into the middle estuary. A, caudavittata is a benthic omnivore, with the 0+ age class ingesting algae and a range of small crustaceans, while older fish prey to a greater extent on polychaetes.     

Aspects of the general biology of Sars' eelpout, Lycenchelys sarsi (Collett, 1871) (Pisces, Zoarcidae), in Oslofjorden, Norway

Biological data on the sizes, age, growth and aspects of the reproduction of Sars' eelpout Lycenchelys sarsi were obtained during a study of the Oslojord fish fauna in 1981. Lycenchelys sarsi is a relatively small zoarcid that occurs on soft sediment. Spawning in the Oslofjord occurs between April and possibly as late as August. This species is typical for zoarcids in that it has a relatively low fecundity (20-40 eggs per female) and the eggs are relatively large (yolked oocytes up to 5.4 mm diameter). Sexual maturity is reached when the fish are approximately 11 cm in total length, corresponding to an age of 3-5 years. The maximum ages of L. sarsi found in the Oslofjord were 6+ years. In general, males reach a larger size than females.