Distribution and population structure of the Chlorophthalmus agassizi (Bonaparte, 1840) on an unexploited fishing ground in the Greek Ionian Sea

The distribution and population structure of the shortnose green eye, Chlorophthalmus agassizi, were studied in the Greek Ionian Sea using data collected during experimental trawl surveys carried out from December 1996 to November 1997. The length–frequency distribution ranged between 45 and 201 mm total length (TL). The significant increase in average size linked with depth has been observed, supporting the general ‘bigger‐deeper’ phenomenon. Specifically, 1528 individuals were measured in the 300–400 m depth zone with a mean TL = 101 mm, 2351 individuals in the 400–500 m depth zone with a mean TL = 132 mm and 1889 individuals in the 500–600 depth zone with a mean TL = 145 mm. Age and growth of the population were determined by otolith readings. Twelve age groups were identified. The von Bertalanffy growth function (VBGF) parameters were L_∞=202.22 mm, K=0.20 and t_o=?1.6 years. Natural mortality was estimated at 0.285 per year, while total mortality was estimated at 0.65. The reproductive period of C. agassizi extends from spring to autumn, with greater activity in the summer.     

Ontogenetic habitat shifts by Galaxias gracilis (Galaxiidae) between the littoral and limnetic zones of Lake Kanono, New Zealand

Synopsis Diel and spatial differences in distribution were determined for the larvae, juveniles, and adults of Galaxias gracilis (Galaxiidae) in a New Zealand dune lake during summer months. Larvae (mostly 10–25 mm TL) and juveniles (25–40 mm TL) inhabited shallow (0–3 m) waters of the limnetic zone and fed predominantly on two limnetic zooplankton species; Bosmina meridionalis and a calanoid copepod. At about 40 mm TL, fish moved from the limnetic to the littoral zone and expanded dietary breadth from two to over seven main prey species, including five species of littoral invertebrates. After reaching a size of about 60 mm TL, most fish moved back offshore to the deeper waters (5–15 m) of the limnetic zone during the day, moving back to the littoral zone at night to feed on invertebrates. The selection of different intra-lacustrine habitats by the various size groups of G. gracilis, and the movements between them, are interpreted as adaptive responses to the interaction between ontogenetic changes in feeding requirements and predation risk.     

Ecology and life history of the clown goby inhabiting the upper Banana River,Cape Canaveral,Florida

Synopsis Monthly collections of clown goby,Microgobius gulosus, were made from March 1984 through February 1985 at two stations located at the head of the Banana River, Brevard County, Florida, as part of the long-term environmental monitoring program at the John F. Kennedy Space Center. A total of 18921 fishes comprising eight families and 12 genera was collected.M. gulosus represented 6.4% of the total catch. Populations ofM. gulosus exhibited aggregation behavior, which varied in intensity depending on densities of individuals m^–2 and habitat characteristics. Capture data were best described by the negative binomial distribution. Mean estimates of individuals m^–2 ranged from 0.0 to a high of 22.1 during periods of peak recruitment. The total length-weight regression for all individuals measured was log₁₀ weight = –4.65 + 2.72 log₁₀ length.M. gulosus obtained a size of 35–40 mm TL the first year and 50–60 mm TL the second year. Total lengths of all specimens ranged from 11 to 71 mm. Young of the year first appeared in May with smallest individuals collected in June and July. A protracted spawning period was observed. Stomach and gut analyses revealed that crustaceans and annelids combined represented 65% and 66% of the total diet forM. gulosus from stations 1 (open) and 2 (impounded), respectively. However, differences in proportions of the two groups were present between the two stations. Crustaceans represented 47.1% of the diet for gobies collected at station 1 and annelids 40.8% for specimens collected from station 2. Fecundity was low with the mean number of ova being 305 ± 77.5 for females between 35 and 49 mm TL. Estimated mortality rate was approximately 95% annually.     

August diet of age-0 Pacific halibut in nearshore waters of Kodiak Island,Alaska

Synopsis The objective of this study was to describe the diet of age-0 Pacific halibut,Hippoglossus stenolepis, for the inshore waters of Kodiak Island, Alaska during August 1991. Stomach contents were identified from 170 age-0 halibut captured inshore of the eastern and southern coasts of Kodiak Island, and were analyzed in relation to halibut size, location, depth and substrate of capture. One hundred sixty-eight of 170 fish had eaten crustaceans, of which the predominant prey taxa were Mysidacea (34.3%), Cumacea (33.1%), Gammaridea (26.6%) and Caridea (3.9%). In five of six capture locations, mysids and amphipods were predominant prey. In the remaining area, Sitkinak Strait, cumaceans were the primary food source. At depths less than 10 m, mysids were the predominant prey taxa. Gammarid amphipods were of primary importance at depths of 10–30 m. Halibut captured from 30–70 m fed mainly on cumaceans. Cumaceans and gammarid amphipods were consumed by halibut caught on gravel substrate. Fish caught on substrates of sand and mud fed mainly on mysids and amphipods. Cumaceans were also consumed on sandy substrates. Fish 45 mm fed on cumaceans. An ontogenetically related shift in diet occurred at 46–55 mm TL, at which size the halibut's primary prey began to shift from cumaceans to mysids. Fish of 46–75 mm consumed increasingly greater proportions of mysids, amphipods and shrimps. The diet of age-0 Pacific halibut along the Kodiak coast during August was related to predator size, and location, depth, and substrate type of capture.     

Population Biology and Growth of Ozark Cavefish in Logan Cave National Wildlife Refuge, Arkansas

Ozark cavefish, Amblyopsis rosae, is a threatened species endemic to the Springfield Plateau of the Ozark Highlands in Arkansas, Missouri, and Oklahoma. One of the largest known Ozark cavefish populations, located in Logan Cave, Arkansas, was surveyed 25 times over a two-year period between 1993 and 1995. During the study, 147 Ozark cavefish > 30 mm (TL) were marked with visual implant tags and 140 Ozark cavefish were available for recapture; 68 were recaptured 189 times and the rest (72) were never recaptured. Individual Ozark cavefish persisted in Logan Cave for a relatively short time. Only 14% of 80 fish tagged during a previous study in 1992 were recaptured during this study, and half of all recaptured fish disappeared within three months. However, if a fish persisted for at least seven months in the cave, its probability of being recaptured over an additional year was high. Maximum persistence of a tagged fish was 28 months, suggesting these fish have a maximum life-span of 4–5 years. Growth averaged 0.6 mm per month, with maximum recorded growth of 6 mm per month and a maximum size of 65 mm TL. Smaller fish grew faster than larger fish but growth rates were sporadic, with several mid-sized fish (45–49 mm) showing little growth (0–3 mm year^-1) while some fish > 50 mm grew up to 12 mm year^-1. Most fish gained in length during April–October, the same period a maternity colony of gray bats occupied the cave. Gross Ozark cavefish movement over the study period ranged up to 1002 m, with a mean movement of 1.2 m day^-1; movement was positively correlated with Ozark cavefish total length. Death seemed the most likely explanation for loss of tagged Ozark cavefish, including fish that emigrated out of the cave. Little up-stream movement was recorded between reaches and did not account for loss of tagged fish. Reproduction within the cave and immigration from the aquifer accounted for persistence of Ozark cavefish in Logan Cave.     

Timing and sites of parturition of the viviparous scorpionfish, Sebastiscus marmoratus

Timing and sites of parturition of the viviparous scorpionfish Sebastiscus marmoratus were investigated both in aquaria and natural habitats of a rocky coast in southern Japan. Females released 4 mm TL larvae during the early night in winter. Night spawning may be advantageous in avoiding predators of both larvae and spawners, because most such predators are inactive during the night. Females inhabiting shallow areas (< 6 m depth) moved to deeper sites for parturition, but ones inhabiting deeper areas (6–8 m depth) gave birth within their usual habitats. This migration may be advantageous in effective larval dispersal.     

Reproductive ecology of red-chinned lizards (Sceloporus undulatus erythrocheilus) in Southcentral Colorado: comparisons with other populations of a wide-ranging species

Summary We studied the reproductive ecology of a population of Sceloporus undulatus erythrocheilus near Walsenburg, CO during the summers of 1987–1990. Reproductive activity commences soon after emergence in early May and continues until the middle of July. Females mature in their second year following hatching at an age of 20–21 months and a size of 60–63 mm snout-vent length (SVL). Two clutches, averaging10.9 eggs, are produced per year. Larger females produce larger clutches with an increase of one egg per 3 mm SVL. Average SVL of females was 71 mm. Eggs are reasonably large (0.32 g) and relative clutch mass was the largest reported for the species (34% of body mass). A principal component analysis was used to examine relationships among reproductive characters in 12 populations of Sceloporus undulatus. The analysis suggested that patterns of reproduction in this wide-ranging species result from several factors reflecting both adaptive and phylogenetic sources of variation.     

Early life history of a seahorse, Hippocampus mohnikei, in Tokyo Bay, Japan

The early morphological development, seasonal and spatial occurrence patterns, and food habits of a seahorse, Hippocampus mohnikei, in offshore waters of Tokyo Bay, central Japan, were studied on the basis of 206 juvenile and young specimens (6.0–65.3 mm TL) collected between August 1995 and January 1999. All the specimens were collected within the period from May to January, inclusive, each year. In the least developed specimen (6.0 mm TL), the number of dorsal, anal, and pectoral fin rays had attained the adult complement, whereas the minute caudal fin, consisting of two rays, was present in juveniles of 6.0–26.4 mm TL. Hippocampus mohnikei≧35 mm TL, being larger than settlement size (ca. 30 mm TL), had very low gut fullness index values (GFI = 0, >70% of specimens), whereas those of 15–29 mm TL had higher values (GFI = 2–4, >80% of specimens). In addition, larger individuals selectively fed on larger planktonic animals (species of Brachyura), which occurred naturally at low densities, although smaller food items, such as Oithona davisae and Penilia avirostris, occurred abundantly, being consumed by smaller H. mohnikei individuals (15–34 mm TL). These results indicated that food availability for H. mohnikei in offshore waters of Tokyo Bay is significant for individuals larger than settlement size, because their food preference would shift from smaller food items to larger food items, which would be scarce in their environments. Received: January 12, 2001 / Revised: May 13, 2001 / Accepted: June 14, 2001     

Breeding biology of the Louisiana red swamp crayfish Procambarus clarkii Girard in Lake Naivasha,Kenya

This paper describes the breeding biology of the Louisiana red swamp crayfish (Procambarus clarkii Girard) that has been introduced in a tropical lake, Naivasha. Notable differences in crayfish biology are found between the place of origin in Louisiana and lake Naivasha.In Naivasha sexual maturity in females is reached at a larger size (42 mm carapace length (CL), 76 mm full length (FL)) than in males (40 mm CL, 71 mm FL). The corresponding figures for Chalmette area of Louisiana are 31–32 mm CL for both sexes and at Ben Hur Research Centre, Louisiana, 33 mm CL. The females weigh between 15 and 20 g at the onset of egg deposition. The corresponding Louisiana values are from 5 to 10 g. Crayfish in Naivasha as in Louisiana breed both inside burrows which are 10–70 cm deep, and on the sediment in shallow water at a depth of between 0.5 and 4 m. These observations suggest that reproduction is very much a lake edge activity. The number of breeding individuals in Naivasha varies with the trend of the water surface level. Sexually active females (form I) as judged from secondary sexual characters (appearance of basal hooks at the base of 3rd and 4th walking legs) persist throughout the year at no less than 60% of the adult male population. This is confirmed by the appearance of recently hatched juveniles (3.4 to 6.5 mm CL) in the water throughout the year. Similarly berried females in Naivasha are found throughout the year, though with peaks at irregular intervals. In Louisiana breeding takes place only from August through November with a single peak in October. The fecundity of crayfish in Naivasha is 433 (SE ± 21, N = 133) and there is a positive correlation between body length and egg number.     

Growth and age structure of the swan mussel Anodonta cygnea (L.) at different depths in lake Mattsee (Salzburg, Austria)

Unionid clams were collected at 1–2 m, 3–4 m and 6–7 m depth in lake Mattsee, a moderately mesotrophic lake, to investigate the effect of depth on clam growth and age structure. No significant differences in age structure of Anodonta cygnea were found (p=0.65). Three and ten years old clams were present at all depths, but in different percentages. Whereas at 1–2 m 13.3% of the collected clams were <4 years old, this percentage was 4.4% at 6–7 m and 7.1% at 3–4 m. A greater percentage (6.7%) of older mussels (9, 10 years) were collected at 6–7 m than at 1–2 m (2.2%). Growth declined with depth. Total length at a given age of clams at 1–2 m and 3–4 m did not differ (p=0.54), whereas differences were significant between clams at 1–2 m and 6–7 m (p<0.05) as well as between 3–4 m and 6–7 m (p<0.05). The Growth constant k was highest at 1–2 m depth.     

Behavioral responses of red hake,Urophycis chuss,to decreasing concentrations of dissolved oxygen

Synopsis Laboratory experiments were conducted to examine changes in behavior of red hake,Urophycis chuss, under decreasing concentrations of dissolved oxygen (DO). Since the ecological requirements of this species change with age, responses were measured for three different groups: (1) age 0+, = 89 mm total length (TL); (2) age 1+, = 238 mm TL; and (3) age 2–3+, = 397 mm TL. As DO decreased from 8–10 mg l^-1 to < 0.5 mg l^-1, changes were evident in active time, water column activity, range of horizontal movement, food searching, and agonistic behavior. Age 0+ fish were most sensitive, moving up into the water column and swimming continuously as DO levels fell below 4.2 mg l^-1. Age 2–3+ fish were the least responsive, remaining on the substrate and increasing only their range of movement at concentrations below 3 mg l^-1. Responses of age 1 + fish were variable, possibly reflecting a transition stage between the younger and older fish. Common to all groups was the decrease and eventual cessation of food searching.     

Reproductive biology of guitar,Rhinobatos hynnicephalus

Synopsis Reproductive biology of the guitarfish,Rhinobatos hynnicephalus, from Xiamen coastal waters is described. Males have two functional testes. Spermatogenic cells in different seminiferous follicles are at different developmental stages while those in the same follicle are at the same stage. The development of claspers suggests that males mature at 380–400 mm TL. Females mature at 390–440mm TL. Both ovaries are functional. The first generation of ovarian eggs reach mature size when 22–24mm in diameter in April or May. The subsequent crop of eggs is ready for ovulation when the intrauterine embryos reach full term. The guitarfish is aplacentally viviparous. Longitudinal folds were observed on the internal wall of the uterus. Gestation takes one year and parturition takes place in June or July. Fecundity ranges from 2 to 9, with the large females usually being more fecund. Of 29 embryos ranging from 52–157mm TL, there were 15 females and 14 males indicating an embryonic sex ratio 1:1.     

Age and growth of tarpon,Megalops atlanticus,larvae in the eastern Gulf of Mexico,with notes on relative abundance and probable spawning areas

Synopsis Leptocephali were collected in June 1981 and July 1989 over the continental shelf and slope of the Florida west coast. Tarpon larvae ranged 5.5–24.4 mm standard length (SL) and were the second most abundant leptocephalus species. Sagittae examined with compound microscopes and scanning electron microscopy had increments that were presumed to be formed daily. Increment counts made using the two microscopic techniques were not significantly different. Estimated ages ranged 2–25 days with a growth rate (± standard error) of 0.92 ± 0.04 mm d^–1 The least squares linear regression equation SL = 2.78 + 0.92 (age in days) best described the relationship between estimated age and length. Adult tarpon appear to undergo a substantial spawning migration from inshore areas frequented during spring and summer to offshore spawning grounds. Spawning occurs during May, June, and July, although the spawning season may be of greater duration.     

Reproduction, population dynamics, growth and production ofScrobicularia plana da costa (pelecypoda) in the Bidasoa estuary, Spain

The breeding cycle, recruitment, population dynamics, growth and production ofScrobicularia plana were studied at one station in the Bidasoa estuary (SE of the Biscay Bay, Spain) during a period of 3 or 4 years. To complete this study, the reproduction for a period of 1 year was analysed at two other sites of the estuary. At none of the stations important differences in spawning activity were observed between the different years. The animals reproduced for the first time when they reached the age of two years. The histological data and the recruitment analysis showed only one spawning period between June and mid-September, with a peak in July-August. This breeding pattern differs from those shown by other southern European populations. The recruitment of spat (0.25–0.50 mm) occurred from June–July to October–December in different years. The population showed different annual patterns of density and population structure, depending on recruitment success. Growth was most rapid in spring and summer. The bivalves reached a mean length of 21.8 mm at the age of approximately 16 months; in the following year they grew to 30 mm. The growth during the life span fitted the theoretical growth equation of Von Bertalanffy. Annual production was in the range of 59.0–83.4 g AFDW m^–2 year^–1. The P/B ratios of the population varied between 0.84 and 1.48 (1.06 ± 1.36; ¯x ± 95% C.I.).     

The effects of traditional gathering on populations of the marine gastropod Strombus luhuanus linne 1758, in southern Papua New Guinea

Summary Little is known of the response of mollusc populations to predation by humans, particularly for tropical species. In this paper, we examine the effects of human predation on populations of the gastropod Strombus luhuanus in Bootless Inlet, Papua New Guinea, by documenting both the population biology of the shellfish and the shell-gathering practices of traditional and contemporary human groups. Strombus luhuanus occurs in local colonies and individuals of each sex from different colonies differed significantly in size. Sexual maturity is reached within two years after settlement, at which time the shell length stabilises at about 35–60 mm, and the shell lip thickens. There was also significant between-colony variation in density (8.35–23.39 individuals/m²), and colonies differed in the depth range of their distributions and the frequency of human collection visits. Traditional gatherers rarely collected individuals which were buried or subtidal. Contemporary collectors used different collecting methods, and gathered subtidal populations to a depth of 2.5 m. Both traditional and contemporary collectors gathered only individuals greater than 30 mm shell length, and in the contemporary sample the probability of being gathered increased significantly with shell length. This was due to size-dependent burying, which was greatest among young juveniles and least among adults. The traditional sample contained fewer shells in the largest size category (>45 mm) and more in the smallest (<40 mm), but this difference largely represents the pooling of shells from different collecting locations rather than widespread juvenisation of colonies due to exploitation. Stromb population densities at collected sites in PNG far exceeded those in comparable uncollected sites in northeastern Australia. We conclude that S. luhuanus displays high resilience to all gathering practices used to date, as a consequence of both its size-dependent burying and partly subtidal distribution, which provide refugia from human predation.     

Notes on the biology of Cancer bellianus (Brachyura, Cancridae) around the Canary Islands

Information on biometric and biological parameters of Cancer bellianus Johnson, 1861 (Crustacea, Decapoda, Brachyura, Cancridae) off the Canary Islands is given. Crabs examined were collected during experimental fishing surveys during 1974–1998. Carapace length, carapace width, total wet weight, sex and ovigerous condition were determined. This species was caught at depths from 153 to 750 m, the deepest ever recorded. Size frequency distributions were assembled and size-weight relationships were estimated by sex. Sex-ratio as a function of size and depth was determined. The size at first maturity was calculated by analysing the relative growth between the carapace length and the left chela width: 103.5 mm CL in males, 101.2 mm CL in females. Ovigerous females, egg size and fecundity estimates are reported apparently for the first time.     

Decomposition of roots and twigs: Effects of wood type (beech and ash), diameter,site of exposure and macrofauna exclusion

Carbon loss and nitrogen dynamics in beech roots (Fagus sylvatica L.), beech twigs and ash roots (Fraxinus excelsior L.) of 0–3, 3–10 and 10–40 mm diameter were investigated during 36 months of exposure in litter bags of 1 and 4 mm mesh. Four experiments were set up: (1) Beech and ash roots (three size classes) were placed in a soil depth of ca 5 cm in a beechwood on limestone; (2) beech twigs (three size classes) were placed on the soil surface of the beechwood; (3) beech roots (3–10 mm) were placed on the soil surface of the beechwood: (4) beech twigs (3–10 mm) were placed on the soil surface of four sites representing different stages of secondary succession (wheat field, 13 year old fallow, ca 50 year old fallow, beechwood). Ash roots generally lost more C than beech roots. Loss in C of ash roots was similar for each of the size classes, whereas in beech roots and beech twigs C loss was in the order large roots > medium roots > small roots. Beech roots (3–10 mm) placed on the soil surface lost considerably less C than beech twigs (3–10 mm). Decomposition of beech twigs varied among ecosystems but generally did not follow clear patterns with successional stages. The fit of linear vs exponential models of decay is compared and in most materials exponential models fitted the data better. In each of the wood materials an accumulation of N occurred. Irrespective of wood type, root and twig diameter, mineralization of N of wood materials placed in the beechwood started uniformly after 12 months. Multiple regression analysis indicated a negative relationship between initial N content and C loss in beech roots and twigs but not in ash roots. The analysis also indicated a significant influence of the degree of white rot and of the amount of mineral soil deposited in the litter bags on C loss of certain wood materials. Generally, mesh size affected C loss and N dynamics only slightly, which is attributed to the comparatively short exposure time.     

Age and growth estimates of the bull shark,Carcharhinus leucas,from the northern Gulf of Mexico

Synopsis Length at age and growth rates for 59 bull sharks, Carcharhinus leucas, collected from the northern Gulf of Mexico were estimated from the band patterns formed seasonally in the vertebral centra. The combined age at length data for both sexes were applied to a von Bertalanffy growth model producing parameter estimates of L = 285 cm TL, K = .076, t₀ = –3.0 yr. Lengths at age for males and females were similar except that males did not attain as great a length as females. Growth was apparently slow and varied among individuals, but in general, was estimated to be 15–20 cm yr^–1 for the first five years, 10 cm yr^–1 for years 6–10, 5–7 cm yr^–1 for years 11–16, and less than 4–5 cm yr^–1 thereafter. Males mature at 210–220 cm TL or 14–15 yr of age; females mature at>225 cm TL or 18+ yr of age. The largest male (245 cm TL) was 21.3 yr old; the largest female (268 cm TL) was 24.2 yr old.     

Temporal distribution and abundance of shrimp postlarvae and juveniles in the mangroves of Muthupet,Tamilnadu, India

The temporal distribution patterns of the predominantly occurring postlarvae and juvenile shrimps in the mangrove and associated habitats of Muthupet, India were investigated for two years from February 1984 to January 1986. Among the eight commercially important species recorded, Penaeus indicus H. Milne Edwards, P. merguiensis De Man, P. monodon Fabricus and Metapenaeus dobsoni (Miers) were predominant. The postlarval recruitment size variedwith species: P. indicus and P. merguiensis recruited at the size of 9–11 mm total length (TL), P. monodon at 12–14 mm TL and M. dobsoni at 4–6 mm TL. The species P. indicus, P. merguiensis and M. dobsoni were observed continuously throughout the study period with maximum abundance occurring from July to September in 1984–85 and from August through October in 1985–86. P. monodon occurred seasonally from November to January in both years. Postlarvae and juvenile catches were low during low salinity and high salinity periods and a higher density was observed in the months of moderate water salinity. Large numbers of P. indicus, P. merguiensis and M. dobsoni clearly showed the preference to the detritus rich muddy substrate, whereas P. monodon did not show any preference and was equally abundant over different substrate types.     

The role of Gloeotrichia echinulata in the transfer of phosphorus from sediments to water in Lake Erken

The abundance of Gloeotrichia echinulata colonies in the sediments of Lake Erken and their phosphorus content were investigated to determine the contribution of Gloeotrichia colonies to total sediment phosphorus. Moreover, the potential size of the algal inoculum and the migration to the water during summer were estimated.The surplus phosphorus content of the resting colonies in the sediment was about 45% of total phosphorus, which maximized at 8.5 µg P (mg dw)^–1 or 81 ng P colony^–1. The C:P ratio (by weight) in the early colonies appearing in the lake water was 50:1, while the ratio stabilized at 150 during the major migration period. The internal supply of surplus phosphorus was used during the pelagic growth of the colonies.The internal phosphorus loading to the epilimnion of Lake Erken due to Gloeotrichia migration could, from the measurements of the increase in particulate epilimnetic phosphorus, be estimated at 40 mg P m ^–2 or 2.5 mg P m^–2 d^–1 in late July and early August. Determination of the number of colonies in the sediment before and during the migration verified this value to be a conservative estimate of the internal phosphorus loading due to Gloeotrichia migration to the epilimnion in Lake Erken.The sediment P content calculated from the P concentration in early epilimnion colonies resulted in a value of 35 µg P (g dw)^–1 as a maximum. This corresponds to only 3% of the total phosphorus content in Lake Erken sediment.