Red snapper (Lutjanus campechanus) demographic structure in the northern Gulf of Mexico based on spatial patterns in growth rates and morphometrics

Red snapper (Lutjanus campechanus) in the United States waters of the Gulf of Mexico (GOM) has been considered a single unit stock since management of the species began in 1991. The validity of this assumption is essential to management decisions because measures of growth can differ for nonmixing populations. We examined growth rates, size-at-age, and length and weight information of red snapper collected from the recreational harvests of Alabama (n=2010), Louisiana (n=1905), and Texas (n =1277) from 1999 to 2001. Ages were obtained from 5035 otolith sections and ranged from one to 45 years. Fork length, total weight, and age-frequency distributions differed significantly among all states; Texas, however, had a much higher proportion of smaller, younger fish. All red snapper showed rapid growth until about age 10 years, after which growth slowed considerably. Von Bertalanffy growth models of both mean fork length and mean total weight-at-age predicted significantly smaller fish at age from Texas, whereas no differences were found between Alabama and Louisiana models. Texas red snapper were also shown to differ significantly from both Alabama and Louisiana red snapper in regressions of mean weight at age. Demographic variation in growth rates may indicate the existence of separate management units of red snapper in the GOM. Our data indicate that the red snapper inhabiting the waters off Texas are reaching smaller maximum sizes at a faster rate and have a consistently smaller total weight at age than those collected from Louisiana and Alabama waters. Whether these differences are environmentally induced or are the result of genetic divergence remains to be determined, but they should be considered for future management regulations.

Survival rates of rays discarded by the bottom trawl squid fishery off the Falkland Islands

Waters off the Falkland Islands are subject to a specialized multispecies ray fishery and were first fished by a Korean fleet in 1989. More than twenty different rajid species have been recorded from catches around the islands, and five species accounted for 87.04% of the total catch during 1993−2002. Catches peaked in 1993 at 8523 metric tons, and specific fishing licenses — R (second season) and F (first season) — were first introduced in 1994 and in 1995, respectively (Agnew et al. 2000; Falkland Islands Government, 2002; Wakeford et al., in press).

The effect of timing of tagging on streamer-tag recapture rates for American lobster (Homarus americanus)

Streamer tags are commonly used to study the ecology and population biology of the American lobster (Homarus americanus). Aquarium observations suggest that streamer tag loss, either through tag-induced mortality or tag shedding, is related to the molt stage of the lobster at the time of tagging, and the molting event itself. Tag-induced mortality, where lobsters did not molt, occurred within eleven and sixteen days following tagging for lobsters tagged in postmolt (4%) and late premolt (10%) stages, respectively; whereas no lobsters tagged in early premolt or intermolt stages died. Taginduced mortality at time of molting was observed for lobsters tagged in late premolt stage (11%), and tag shedding was observed for lobsters tagged both in early (25%) and late premolt (11%) stages, but was significantly higher (P=0.014) for lobsters tagged in early premolt stages. Autopsies revealed that lobsters died mainly of organ perforations (hepato-pancreas and pericardial sac) following the tagging process, and rupture of the dorsal thoraco-abdominal membrane during the molting process. The total tag loss was estimated at 4% for lobsters tagged after molting, and 27% and 31% for lobsters tagged in early and late premolt stages, respectively. There was no tag loss for lobsters tagged in the intermolt stage during four months of laboratory observations (July−October). To minimize streamer tag loss, lobsters should be tagged during the intermolt or postmolt stage. Based on field studies, recapture rates for lobsters tagged in premolt stage are always lower than those of lobsters tagged in postmolt stage. Furthermore, recapture rates during the second year, for lobsters that molt in the year following tagging, were drastically reduced, and no lobster was recaptured after four years at large. Finally, to account for tag loss during the first year at large, a minimal adjustment of 24.9% (SD 2.9%) and 4.4% (SD 1.6%) for the recapture rate of lobsters tagged immediately before and after the molting season, respectively, is recommended. Adjustments beyond one year at large are not recommended for the American lobster at this time.

A new growth model for red drum (Sciaenops ocellatus) that accommodates seasonal and ontogenic changes in growth rates

The red drum (Sciaenops ocellatus) is a popular gamefish found throughout the coastal waters of the Gulf of Mexico and along the eastern seaboard as far north as Massachusetts. Juvenile red drum grow extremely rapidly, especially during the warmer months, but adults grow very little. In fact, the change in growth with age is so abrupt that the standard von Bertalanffy curve has proven inadequate— the predicted lengths of younger fish are generally too large and the predicted lengths of older fish too small (see Beckman et al., 1988; Murphy and Taylor, 1990).

Food habits and consumption rates of common dolphinfish (Coryphaena hippurus) in the eastern Pacific Ocean

An ecosystem approach to fisheries management requires an understanding of the impact of predatory fishes on the underlying prey resources. Defining trophic connections and measuring rates of food consumption by apex predators lays the groundwork for gaining insight into the role of predators and commercial fisheries in influencing food web structure and ecosystem dynamics.We analyzed the stomach contents of 545 common dolphinfish (Coryphaena hippurus) sampled from 74 sets of tuna purse-seine vessels fishing in the eastern Pacific Ocean (EPO) over a 22-month period. Stomach fullness of these dolphinfish and digestion state of the prey indicated that diel feeding periodicity varied by area and may be related to the digestibility and energy content of the prey. Common dolphinfish in the EPO appear to feed at night, as well as during the daytime. We analyzed prey importance by weight, numbers, and frequency of occurrence for five regions of the EPO. Prey importance varied by area. Flyingfishes, epipelagic cephalopods, tetraodontiform fishes, several mesopelagic fishes, Auxis spp., and gempylid fishes predominated in the diet. Ratios of prey length to predator length ranged from 0.014 to 0.720. Consumption-rate estimates averaged 5.6% of body weight per day. Stratified by sex, area, and length class, daily rations ranged up to 9.6% for large males and up to 19.8% for small dolphinfish in the east area (0–15°N, 111°W–coastline). Because common dolphinfish exert substantial predation pressure on several important prey groups, we concluded that their feeding ecology provides important clues to the pelagic food web and ecosystem structure in the EPO.

Mortality rates of the Poovalan prawn (Metapenaeus dobsoni) along the southwest coast of India with a note on the dynamics of its population

The annual instantaneous total mortality coefficient (Z) for the prawn Metapenaeus dobsoni has been estimated to range from 0.8 to 5.14 by the cumulative catch curve method. Different methods used in the study resulted in wide ranging values of natural mortality (M) (0.6 to 2.303), but the yield per recruit model when superimposed with the absolute yield values revealed the right order to be > 2. The biologically optimum yield of about 18 thousand tons is obtained for an effort of 2,702 trawlers per day for 215 fishing days when the annual exploitation ratio (E) is about 52%.

Studies on the filtration, feeding and excretion rates in Perna viridis, Marcia cor and Crassostrea gryphoides (Mollusca: Bivalvia) using P³² labelled Ankistrodesmes

The study deals with a series of experiments to investigate feeding and excretion in three species of bivalves: Perna viridis (Linné), Marcia cor (Sowerby) and Cassostrea gryphoides (Gould) from Manora Channel, Karachi. Bivalves were fed with suspensions of Ankistrodesmes labelled with P³². These animals showed a considerable variation in the average filtration rates depending upon species and the body lenght. Exceptionally high content of the P³² introduced with Akistrodesmes, got excreted as pseudofaeces and faeces within first three days following its absorption as a meal. The assimilated P³² is partly released as faecal material and its major proportion is directly transferred to the solution. As expexted the gonad and kidney are the main organs found responsible for excretion as comared to other body parts. Although, the assimilated P³² is mostly concentrated in the digestive glands, the results also show a significant presence of P³² in the gonads. Accumulation of P³² was the least in the foot.

Mortality rates estimates for Metapenaeus monoceros (Fabricius) of Maputo Bay

The species Metapenaeus monoceros in Maputo Bay recruits to the fishery almost all over the year, but the main recruitment occurs over a short period of time, each year, during April-May. Growth curves were constructed by following the progression of modes over a period of time. The von Bertalanffy growth parameters were estimated as L∞=31.9 mm and K(monthly)=0.25, for males, and L∞=48.3 mm and K(monthly)=0.14, for females (Brinca and Sousa, 1984). Using data on growth and length composition of the catches, the following methods were applied to estimate mortality rates of M. monoceros: estimation of natural mortality by using approximative methods; use of c.p.u.e. data; catch curves; cohort analysis; average age and length methods.

Studies on the occurrence and growth rates of two intertidal fouling bryozoans in the Mattancherry channel of Cochin harbour, south-west coast of India

Occurrence and growth rates of two species of intertidal fouling bryozoans namely Electra bengalensis (Stoliczka) and Electra crustulanta (Pallas) are presented in this paper. The former was a typically marine form, settling on panels only during the high saline conditions of the pre-monsoon period and were absent during the low salinity conditions of the monsoon period, while the latter appeared to be a typical brackish water form settling on panels during the low saline conditions existing during the monsoon and post-monsoon periods and were totally absent during the pre-monsoon months. Regression co-efficient of the former was higher than that of the latter suggesting more pronounced growth in Electra bengalensis. Maximum growth for this species was noticed during March, April and May (pre-monsoon) while for the other species growth was more or less similar during monsoon and post-monsoon months (June-January) showing that the species was at home in oligohaline and mesohaline waters.

The effect of various protein levels on the growth and survival rates of Penaeus monodon Fabricius

Postlarvae of tiger prawns, P. monodon , were fed with various protein levels of 0; 30; 40 and 50%, fish meal and rice bran were combined and pelletized for 16 wks. Prawns used had an average mean length of 1.2 mm and an average mean weight of 5.5 mg. Nitrite, ammonia, dissolved oxygen content, temperature and pH were monitored. After one month of feeding, growth increments of postlarvae fed with 30% protein diet were significantly different from those given 0; 40 and 50%. Survival rate of the group fed 40% protein was higher (81.7%) but was not significantly different from those fed 30% (68.0%). The highest feed efficiency was obtained from the 30% protein pellets (4.6). At the end of 16 weeks, growth increment of 40% protein level was significantly different from the 30% and 50% protein levels, but the survival rate was not signficantly different from the 30% protein level. Feed conversion for the 40% protein diet was 2.8.

Survival rates of different postlarval stages of Penaeus monodon Fabricius

The objective of this study is to determine survival rates of different postlarval stages upon stocking in the Leganes ponds. Twelve 3m x 2m x 2m suspension nets made of nylon cloth (mesh size = 0 . 1 mm) were set up in a Leganes Station pond (ave. water depth = 1 m) by means of 3-m long poles stacked at distances approximating the area of each net. The net bottom was filled with topsoil at least 15 cm thick to stimulate the pond bottom. At least 60 cm of the upper edge of each net was above the water level to prevent mixing of water inside and outside the net. P.monodon of stages P SUB-11 , P SUB-15 , P SUB-21 (from the hatchery) and P SUB-25 (from the wet lab) were stocked in the nets at 200/sq m or 1,200 fry/net. Due to lack of fry, only one P SUB-25 net was stocked. Each net had two large dried miapi branches as shelter from predation and cannibalism for the young sugpo fry. Fresh lablab was fed at the rate of one pail (approximately 5 kg) every four days per net. Harvest data show relatively higher survival rates for P SUB-15 and P SUB-18 compared to P SUB-11 and P SUB-25 with no significant difference between these two stages. The results for P SUB-25 may not be valid because the stock came from the wet lab in comparison to the other postlarval stages which were reared in the hatchery. Moreover, the P SUB-25 stock had no replicates and the net itself (no. 10) was discovered to have many holes. These preliminary results point to P SUB-15 as the best stage for harvest from the hatchery in terms of high pond recovery and lesser expense in rearing compared to older postlarvae.

Studies on the egg quality of Penaeus monodon Fabricius based on morphology and hatching rates

Eggs of P. monodon are classified into 5 different types on the basis of morphological criteria and hatching rates: A sub(1) eggs, which undergo normal development with 58% hatching rate; A sub(2) eggs, which show delayed and/or abnormal development with 32% hatching rate; B eggs, which are unfertilized and characterized by irregular cytoplasmic formation; C eggs, which are unfertilized and show no change in appearance; and D eggs, which are unfertilized and show extensive bacterial presence. The establishment of a highly linear relationship between percent A sub(1) eggs and hatching rate provides a useful tool to aid the hatchery technician in determining which spawnings to reject outright and which to rear through the larval and post-larval stages.

Growth and survival rates of hatchery-produced and wild milkfish fry grown to fingerling size in earthen nursery ponds

Growth and survival rates of hatchery-produced and wild milkfish (Chanos chanos ) fry grown to fingerling size were compared. Data show no significant difference between the 2 fry. At a recommended stocking density of 30 fry/m super(2), hatchery-produced milkfish fry could attain fingerling size of almost 2g with a survival of 68%. The study indicates that hatchery-produced fry/fingerlings can equal the culture performance of the wild fry. Comparative performance of hatchery-bred and wild fry should encourage intensified research on milkfish broodstock development and refinement of induced spawning methods.