Some aspects of the ecology of the leatherback turtle Dermochelys coriacea at Laguna Jalova, Costa Rica

The ecology and reproductive biology of the leatherback turtle (Dennochelys coriacea) was studied on a high-energy nesting beach near Laguna Jalova, Costa Rica, between 28 March and 8 June 1985. The peak of nesting was between 15 April and 21 May. Leatherbacks here measured an average 146.6 cm straightline standard carapace length and laid an average 81.57 eggs. The eggs measured a mean 52.12 mm diameter and weighed an average of 85.01 g. Significant positive relationships were found between the carapace lengths of nesters and their clutch sizes and average diameter and weight of eggs. The total clutch weighed between 4.02 and 13.39 kg, and yolkless eggs accounted for an average 12.4% of this weight. The majority of nesters dug shallow (<24 cm) body pits and spent an average 81 minutes at the nest site. A significant number of c1utcbes were laid below the berm crest. In a hatchery 42.2% of the eggs hatched, while in natural nests 70.2% hatched. The average hatchling carapace length was 59.8 mm and weight was 44.6 g. The longevity of leatherback tracks and nests on the beach was affected by weather. One nester was recaptured about one year later off the coast of Mississippi, U.S.A. Egg poaching was intense on some sections of the Costa Rican coast. Four aerial surveys in four different months provided the basis for comparing density of nesting on seven sectors of the Caribbean coast of Costa Rica. The beach at Jalova is heavily used by green turtles (Chelonia mydJJs) after the leatherback nesting season. The role of the Parque Nacional Tortuguero in conserving the leatherback and green turtle is discussed.(PDF file contains 20 pages.)

Some aspects of the limnology of Makwaye (Ahmadu Bello University) Lake, Samaru, Zaria

The monthly variations in the physico-chemical parameters and zooplankton abundance were followed from December, 2003 to March 2004 in Makwaye (Ahmadu Bello University Farm) Lake, Samaru, Zaria. In this lake, all physico-chemical parameters investigated showed wide variations within the months except hardness, which exhibited highly significant variation both between stations and within months. Chemical variables including Na, Mg, Zn, Pb, Fe, K and Cu showed significant variations within the months. Three groups namely Cladocera (32.62%), Rotifera (29.33%) and Copepoda (38.05%) were observed. These indicated low species richness

Some aspects of the ecology of the limnoplankton, with special reference to the phytoplankton. [Translation from: Svensk Botanisk Tidskrift 13(2) 129-163, 1919.]

This paper tries to develop more generally some fundamental bases for the ecological study of freshwater plankton. A special attention is given to the phytoplankton associations which can be separated out and made into groups according to their dependence upon changing environments. Plankton formations in different types of water bodies (ponds, lakes and rivers) are studied.

Fundamental aspects of the feeding of the amphipod Gammarus (R.) balcanicus (Crustacea, Amphipoda). [Translation from: Nauchn.Dokl.vyssh.Shkoly (Biol.Nauk) 1970(7) 12-16, 1970]

The amphipods are major food items for many commercial fishes, and they are used as protein food for agricultural animals. In the present paper are presented the results of four-year observations on the feeding of Gammarus balcanicus in nature and in an aquarium. Among the studied aspects were the dependence of daily food ration on sex and physiological state (with and without eggs) and feeding on different kinds of plant food. The study concludes that Gammarus balcanicus willingly feed on soft half-decayed plant residues; into their ration also enters food of animal origin. In contrast to other amphipods, G. balcanicus eats representatives of its own species very rarely, and only dead or immobile ones.

Aspects of the washout of salmonid eggs. 2. Effects of drifting on development and survival of eggs of brown trout (Salmo trutta L.)

At high stream discharges salmonid eggs can he displaced from the gravel and may drift downstream. It has been suggested that developing salmonid eggs may be killed by ”physical shock”, especially during the period before ”eyeing”. Similarly, a progress report by the International Pacific Salmon Fisheries Commission (1966) states that salmonid eggs are most sensitive during the period between fertilisation and blastopore closure. However, it would seem unlikely that this sensitivity actually begins at the time of fertilisation because, in nature, a period, perhaps measured in hours, must occur during which the newly-fertilised eggs are exposed to physical shock during the deposition of gravel over them as a result of the cutting activity of the female fish. The present report describes simple channel experiments designed to answer the two questions: 1. After release of eggs from the gravel, does the process of drifting downstream, which implies some physical shock through movement and impact, decrease the survival of salmonid eggs? 2. Is the survival rate-influenced by the stage of development of the eggs?

Interpreting the environmental record in the sediments of Blelham Tarn

Two aspects of the environmental record in the sediments of Blelham Tarn have been investigated: (1) the ecological history of the catchment, and lake-catchment relationships, by detailed analysis of the preserved pollen (as an indication of vegetation) and sediment composition with respect to a range of inorganic and organic geochemical variables and (2) a detailed investigation of the manner in which sediment is being formed today, including the way in which microfossils (pollen and diatoms) are being recruited and incorporated into sediments. When the record was examined by biological and geochemical analysis, together with radionuclide dating, of closely spaced samples, it was found that the changes of the last 30 yrs represented only the most recent episode in a long history of modification of the lake by man. To find an approach to this it is necessary to go back for at least 2500 yrs.

Physiological aspects of the life cycle of the river lamprey, Lampetra fluviatilis L

The life cycle of the river lamprey, L. fluviatilis, is reviewed. The larval lamprey, or ammocoete, is a blind, filter-feeding animal, which normally lies concealed in the silt deposits of streams and rivers. After a period of 3-5 years in fresh water the ammocoete undergoes a metamorphosis in the summer months into a sexually immature, non-feeding stage known as the macrophthalia, which is active. This stage migrates downstream in late winter. It adopts a parasitic existence, in intertidal areas. After 18 months it returns to spawn in fresh water, after a final freshwater stage lasting up to 9 months. The river lamprey dies within a few days after the spawning period of 3-4 weeks, and none survive to spawn the following year.

Aspects of the washout of salmonid eggs. 6. Information on gravel composition , redd sites, the dimensions of redds and the depth of egg burial

Sampling was concentrated on the North Moor region and the series of ditches which drained this area to the Bristol Channel. Although most ditches were not deep the mud substratum precluded sampling from within the habitat. All samples were taken with a pond net from the banks. Efforts were made to sample each part of the habitat although in some ditches the macrophyte growth was so intense as to make sampling difficult particularly of the sediments. Organisms were identified on the 10 sampling sites.

Aspects of the washout of salmonid eggs. 4. Effects of a standard mechanical shock, applied at different stage of development, upon survival and development of eggs of brown trout (Salmo trutta L.)

It is generally accepted by fish culturists that salmonid eggs are sensitive to mechanical shock and that the sensitivity varies with the stage of development of the eggs. In general, the period of greatest sensitivity is thought to occur between fertilization and ”eyeing”. However, it is reasonable to expect that, during a period (perhaps of several hours) following fertilization, sensitivity will be low because in nature during this period the eggs may be subject to some mechanical shock caused by the parent fish covering them with gravel. In 1983-4 and 1984-5 experiments were performed on brown trout (Salmo trutta L.) eggs to examine the effect of a standard mechanical shock (c. 2,500 eggs in 1983-4 and c. 8,400 eggs in 1984-5) at various stages of development upon survival to hatching and time of hatching.The results of these experiments are reported in this study.

Use of Fish Corrals in the Seine Fishery of the Virgin Islands

Although selected aspects of the commercial fishery in the Virgin Islands have been documented since the early 1930's (Fiedler and Jarvis, 1932; Idyll and Randall, 1959; Hess, 1961; Swingle et al. 1970; Brownell, 1971; Brownell and Rainey, 1971; Sylvester and Dammann, 1972, and Olsen et al., 1978), fish corrals and their use have not been described. This account, based on personal observations made during 1985-86, summarizes commercial fishing methods in the Virgin Islands (U. S. and British), documents the use of fish corrals, and serves as an introduction to the methodologies of this harvesting technique. Interviews of commercial fishermen about how and when fish corrals are used provided information not available from direct observation. Local common names for gear type and fish species are shown in parentheses.