The Biology Of The Ray’s Bream, Brama Brama, From The Yorkshire Coast And Central North Sea : Scarborough Data.
D. E. WHITTAKER
A prominent characteristic of the fish fauna of the North Sea coast of the British Isles, from Scotland to Suffolk, and particularly of the Yorkshire sector, is the occurrence of the oceanic, mesopelagic Brama brama, the Ray’s Bream, first recorded as a British fish at Middlesborough Marsh on Teeside in 1681 by Ray and Willughby.
Ray’s Bream is a typical member of the family Bramidae, characterised by their deep, laterally compressed bodies, covered in large, brightly silvered scales. The pelvic fins are small, but the pectorals are very long and blade-like, while the caudal fin is long and deeply cleft. Internally, the gut is short, and provided with a few very large pyloric caecae.
Ray’s bream is found commonly in deep-water in the Western Mediterranean, in the Atlantic off Madeira, Spain and Portugal, and each summer migrates north, to the west of Ireland, as far as Norway. It is known to be predated on, in these mesopelagic depths, by sharks including Centrophorus squamosus.
The numbers of Ray’s bream penetrating south into the shallow North Sea basin, however, are not constant, with the fish sometimes going unrecorded for many years. Alternatively, the fish periodically and inexplicably shows great incursions and increased frequency into the North Sea basin, and these events may sometimes extend over several consecutive years.
Particularly good years of greater migration into the North Sea were in the 1920’s, peaking in 1927 and 1928, and again in the late 1940’s and ‘50’s, peaking in 1952, but historically, the events of the greatest magnitude have occurred within the last 40 years.
Causal Factors Of Ray’s Bream Events In The North Sea Basin
The nature of these “Rays Bream events” down the east coast and their causal factors is not understood, and a number of biological and physical components have been suggested as being involved in their creation, including:-
i) Periodic successful spawning and larval survival years in their home waters, giving rise to a number of heavy year-classes of the fish which then become more numerous and noticeable in their northward migration, with subsequent mass penetration of the North sea.
ii) Unusual hydrographic conditions that cause large runs of a normal population of the fish from the Atlantic into the North Sea.
iii) A combination of these two components, when years of increased stocks of the fish also coincide with years of increased Atlantic inflow into the North Sea.
iv) A useful study by the researchers Mead and Haedrich (1965), who gathered all the known northern occurrences of the fish up to that time, postulated that Rays’s Bream is limited in distribution to waters warmer than 12.5 degrees Centigrade, and could not survive in temperatures below 10 degrees Centigrade.
A study of the data accumulating since 1965 reveals problems of consideration of any of these factors, and the nature of these Ray’s Bream events is evidently more complex.
Ray’s Bream Events Since 1965, Scarborough Data.
No local records of the fish are known for 1965 or 1966, but since the inception, by the author, of the Yorkshire Rare Fish Recording Scheme at Scarborough in 1967, enlisting the daily retention and collection of rare and unusual fishes from the Scarborough fleet, all specimens of Brama caught by fishing gear have been recorded, with the local beaches also being monitored for their occurrence by stranding. The accumulated records therefore illustrate the relative frequency of occurrence, together with the length distributions, of Ray’s Bream occurring on the Yorkshire coast, from 1967 to 2011.
Until recent years, the greatest recorded run of the fish into the North Sea began in 1967, the numbers increasing year upon year until the peak of the mid 1970’s, following which the migrations fell away to a cessation of records in 1983.
Occurrences of the fish were rarely recorded in the following 20 year period until their comparative reappearance in 2005, their virtual absence from the North Sea during this period resulting in many east-coast fishermen only recently encountering the fish for the first time in their fishing careers. Since 2005 the numbers of fish occurring in each succeeding year have once again continued to increase in a repetition of the events of the late 60’s and early 1970’s.
The numbers of fish recorded in the autumn/winter of 2009/10 are therefore, as expected, greater than those of the corresponding 2008/9 season, and both these latter periods are at least equally comparable in magnitude to the 1975/6 and 1976/7 peak years.
A direct comparison of the Yorkshire records between these two time periods is not possible, because of the collapse, since the late 1980’s, of trawling effort by the Scarborough fleet, a daily and primary source of numerous records of rare and unusual fish records. Returns from the present day fleet are therefore considerably reduced.
However, the records accumulating from other methods of monitoring the fish are comparable, and together with the background of recent anecdotal reports from along the coast, confirm that the magnitude of the 2009/10 incursion is historically the greatest of the fish to have occurred, and exceeds that of the 1975-7 maximum. While it is possible that the 2009/10 Brama season may have seen the peak of the current cycle, with numbers of the fish beginning to fall away in forthcoming seasons, it is equally possible that the incursion cycle has not yet attained its maximum, in which case the numbers of Brama occurring on the Yorkshire coast in 2010/11 will be phenomenal.
The length (age) distribution of the fish occurring recently, compared to those of the earlier period, is very different, the fish being much smaller than the very large fish occurring through the 1970’s.
Sampling Of Ray’s Bream
Recording of Brama brama each year has followed a standardised method of biological sampling to give comparative results throughout the ongoing sequence of data:-
The weight of all whole fish is measured in grams.
The total length, measured in millimetres, is that from the snout to the extreme tip of the closed, outstretched, longest lobe of the caudal fin.
NB The caudal fin of Brama is extremely variable; in some fish its proportion is noticeably large in comparison to the total length of the fish, and this fin is also frequently asymmetrical, with either dorsal or ventral lobe being longer than the other. Standard length only has therefore been used to compare the yearly length distributions and for other comparative and statistical work.
The standard length is recorded as that from the snout to the terminal ventral margin of the caudal peduncle.
Buccal and branchial cavities are examined for parasites.
Gills are then removed and preserved for later parasite investigation.
Otoliths for age studies are removed, washed in distilled water, followed by acetone, and stored in tubes. Otoliths of Brama are difficult to interpret and it has been found useful to scorch some otoliths to a dark brown colour before examination in one of the usual clearing media or mounting in DPX.
Viscera are examined in situ and then removed, stomach contents are examined and the stomach preserved with the gut for later parasite investigation.
The fish is sexed and ovaries weighed and preserved for later examination.
Fish recovered from the beaches are frequently damaged by birds, but such material not only forms part of the yearly monitoring of the numbers of fish occurring, but is still invaluable for providing data since at the very least the important standard length can be recorded and otoliths obtained. Although under such conditions the viscera may reveal parasite infection data.
Feeding And Prey Of BRAMA BRAMA Off The Yorkshire Coast
All Brama examined on the Yorkshire coast are fine, heavy, healthy fish, that appear to be well fed, probably following heavy feeding activity during the summer period, when the fish escapes notice due to the absence of any local fishery using pelagic gear that will select and reveal its presence at this time.
Only in 1976 and 1977 when numerous boats along the coast converted their fishing gears for participation in the increased sprat fishery of that time, was a suitable pelagic fishery present to reveal the presence of the fish, high in the water column, on the Yorkshire grounds. A Russian sprat-fishing vessel, one of many present off the Yorkshire coast in 1976, was observed to have strings of split and salted Brama hanging up to dry on deck.
Brama caught in the sprat fishery at that time were gorged chiefly upon sprats, Sprattus, but young mackerel, Scomber, herring, Harengus, and whiting, Merlangius, were also found in stomach contents. Other prey items recorded included euphausiids and 0-group stages of the grey gurnard, Eutrigulus.
Although most autumnal and winter fish of the 2009/10 incursion were, as usual, devoid of stomach contents, a small proportion of the fish have been found to be still actively feeding into January 2010, despite the low temperatures. Prey items have again included euphausiids and clupeids, together with Scad, Caranx, and Sepiola, and more frequently, small squid [Loligo or Alloteuthis].
What would seem a very unusual prey item for Brama, an adult dragonet, Callionymus, was found in the stomach of a fish taken at Scarborough in January 2010.
Temperature Cropping Of BRAMA BRAMA
As noted above, there are no pelagic fisheries operating off the Yorkshire coast to reveal the presence of the fish in the warmest period of late summer, when the fish will be most active, and when a review of the records, as shown by Mead and Haedrich, suggests that the fish, in some years at least, should be present in the Central North Sea. Historically, records of Brama in the area only begin to accumulate with the progressive autumnal fall in sea temperatures, the probable reason for a proportion of the fish becoming more susceptible to capture by static demersal fishing gears such as trammels and gill-nets, slow-moving demersal trawls, and by stranding on gently sloping, sandy beaches during this period of decreasing sea-temperatures.
The effect of falling temperatures on Brama is not immediate and catastrophic, but is protracted over many weeks, with fish continuing to be stranded through January and into mid February 2010, when sea temperatures are considerably below the tolerance parameters concluded by Mead and Haedrich, and a noticeable later time-shift in the fall-out period of Brama is demonstrable in the records between the cycle of 1967-1982 and that of the present cycle, 2005-(2010).
Parasite Fauna Of Yorkshire BRAMA BRAMA
A number of parasitic taxa have been recorded from the several hundred Brama that have been examined in the Scarborough district.
The free-swimming copepod Caligus is frequently encountered in the buccal cavity and inside the opercula, and has also been found to be present in some numbers on the external surface of those fish recovered immediately on stranding. No sessile parasitic copepoda have been encountered.
The gill axils and tissue covering the cleithrum and branchiostegals are frequently infected with didymozoon monogenean trematodes, including Koellikeria filicollis, with very large encysted females sometimes being present. More infrequently, the tissue of the anterior wall of the pericardium is also infected. Another monogenean trematode, Octodactylus, is the only parasite recorded from the gills of the Yorkshire fish, but is extremely rare.
Tetraphyllidean cestode larvae are present in the gastro-intestinal tract of most fish. No adult cestodes have been found. The musculature of the majority of Brama examined has been infected with the large larvae of the Lacistorhynchid cestode Floriceps gigas.
Nematodes, including Thynnascaris and Hysterothylacium are surprisingly infrequent and infection rates always low.
Infections by digenean trematodes , although commonly encountered in most fishes, have rarely been found in Yorkshire specimens of Brama, despite the large number of fish examined.
Species of Acanthocephala are also rare. Single specimens of a species of Echinorhynchus , unusual for its vivid colouration, occurring in the coelom of Brama in 1976 and 2011, are the only adult acanthocephala recorded and is a very rare infection. Larvae of Bolbosoma have also been recorded.