The Nile perch fishery: traditional and emerging fisheries, overfishing and the use of illegal gears on Lake Albert

The fisheries of Lake Albert have come under increasing focus due to several driving forces that have synergistically evolved resulting into concerns from diverse stakeholders. The driving forces include: the commercialization of the fisheries with entry into the value chain of industrial fish processing, a decline in fish stocks especially of the large-size fishes and the emergency of the light - fishing targeting small pelagic fishes. In addition, the assumption by some opinion leaders that light-fishing (use of light) has destroyed the Nile perch fishery of Lake Albert, other factors such as cross-border fishing conflicts, the emergence of oil, an influx of traders in fish-related activities, and the limited regulatory and enforcement regimes for the diverse commercially exploited fish fauna of Lake Albert all require continuous information and action.

Interim report on the progress of an inventory of artesian wells in Florida: leading to the enforcement of sections 370.051 - 370.54, Florida statues

One of the causes of lower artesian pressure, water waste and aquifer contamination is the misuse and insufficient care of artesian wells. In 1953, Senate Bill No. 57, entitled "An Act to Protect and Control the Artesian Waters of the State" (see Appendix) became a law. This law was passed through the efforts exerted by leading members of the Senate and the House of Representatives, who understood the need for a wise and controlled expenditure of our most valuable natural resource. The State Geologist and his authorized representatives were designated by this law to enforce this conservation measure; however, no financial provision was included for the 1953-55 biennium. The proposed program of the Florida Geological Survey for this biennium did not include the funds nor provide any full-time personnel for the enforcement of this statute. As a result, little actual work was accomplished during these two years, although much time was given to planning and discussion of the problem. Realizing that this program could provide additional basic data needed in the analysis of the water-supply problem, the State Geologist sought and was granted by the 1955 Legislature adequate funds with which to activate the first phase of the enforcement of Florida Statute No. 370.051-054. Enumerated below is a summary of the progress made on this investigation as outlined previously: 1. Data have been collected on 967 wildly flowing wells in 22 counties. 2. Chloride determinations have been run on 850 of the 967 wells. 3. Of the 967 wells, 554 have chlorides in excess of the 250 ppm, the upper limit assigned by the State Board of Health for public consumption. 4. Water escapes at the rate of 37, 762 gallons per minute from these 967 wells. This amounts to 54, 377, 280 gallons per day. The investigation is incomplete at this time; therefore, no final conclusions can be reached. However, from data already collected, the following recommendations are proposed: 1. That the present inventory of wildly flowing wells be completed for the entire State. 2. That the current inventory of wildly flowing wells be expanded at the conclusion of the present inventory to include all flowing wells. 3. That a complete statewide inventory program be established and conducted in cooperation with the Ground Water Branchof the U.S. Geological Survey. 4. That the enforcement functions as set down in Sections 370.051/.054, Florida Statutes, be separated from the program to collect water-resource data and that these functions be given to the Water Resources Department, if such is created (to be recommended by the Water Resources Study Commission in a water policy law presented to the 1957 Legislature). 5. That the research phase (well inventory) of the program remain under the direction of the Florida Geological Survey. (PDF contains 204 pages.)

No evidence of bias from fish behavior in the selectivity of size and sex of the protogynous red porgy (Pagrus pagrus, Sparidae) by hook-and-line gear

Most fisheries select the size of fish to be caught (are size selective), and many factors, including gear, market demands, species distributions, fishery laws, and the behavior of both fishermen and fish, can contribute to that selectivity. Most fishing gear is size-selective and some, such as gill nets, are more so than others. The targeting behavior of fishermen is another key reason commercial and recreational fisheries tend to be size-selective. The more successful fishermen constantly seek areas and methods that yield larger or more profitable sizes of fish. Fishery regulations, especially size limits, produce size-selective harvests. Another factor with the potential to cause selectivity in a hook-and-line fishery is the different behavioral responses of fish to the bait or lure, whether the different responses arise among different fish sizes or between the sexes.

Movements, behavior, and habitat selection of bigeye tuna (Thunnus obesus) in the eastern equatorial Pacific, ascertained through archival tags

Ninety-six bigeye tuna (88– 134 cm fork length) were caught and released with implanted archival (electronic data storage) tags near fish-aggregating devices (FADs) in the equatorial eastern Pacific Ocean (EPO) during April 2000. Twenty-nine fish were recaptured, and the data from twenty-seven tags were successfully downloaded and processed. Time at liberty ranged from 8 to 446 days, and data for 23 fish at liberty for 30 days or more are presented. The accuracy in geolocation estimates, derived from the light level data, is about 2 degrees in latitude and 0.5 degrees in longitude in this region. The movement paths derived from the filtered geolocation estimates indicated that none of the fish traveled west of 110°W during the period between release and recapture. The null hypothesis that the movement path is random was rejected in 17 of the 22 statistical tests of the observed movement paths. The estimated mean velocity was 117 km/d. The fish exhibited occasional deep-diving behavior, and some dives exceeded 1000 m where temperatures were less than 3°C. Evaluations of timed depth records, resulted in the discrimination of three distinct behaviors: 54.3% of all days were classified as unassociated (with a floating object) type-1 behavior, 27.7% as unassociated type-2 behavior, and 18.7% as behavior associated with a floating object. The mean residence time at floating objects was 3.1 d. Data sets separated into day and night were used to evaluate diel differences in behavior and habitat selection. When the fish were exhibiting unassociated type-1 behavior (diel vertical migrations), they were mostly at depths of less than 50 m (within the mixed layer) throughout the night, and during the day between 200 and 300 m and 13° and 14°C. They shifted their average depths in conjunction with dawn and dusk events, presumably tracking the deep-scattering layer as a foraging strategy. There were also observed changes in the average nighttime depth distributions of the fish in relation to moon phase.

Final report on an inventory of flowing artesian wells in Florida: leading to the enforcement of sections 373.021 - 373.061 Florida Statutes 1957

This report published as Information Circular No. 21, together with the interim report published in 1957 as Information Circular No. 10, Florida Geological Survey, illustrates as completely as possible the situation that now exists among the freely flowing wells of the State. (PDF contains 40 pages.)

Spawning of yellowfin tuna and the discrimination of subpopulations

ENGLISH: The spawning of yellowfin tuna (Thunnus albacares) in the eastern Pacific Ocean was examined to ascertain the existence of separate subpopulations within this area. Investigations of biochemical genetics of yellowfin indicate that there are a number of genetically distinct groups in the eastern Pacific. In addition, yellowfin belong to two recruitment cohorts, X and Y, which are composed of a mixture of these genetically different groups. Spawning data were collected from 1956 through 1961 from the coastal fishing grounds, and from 1970 through 1973 from the offshore fishing areas. Temporal and spatial aspects of spawning of the fish of the two cohorts were analyzed to determine if yellowfin spawning behavior supports the existence of genetically separate subpopulations. Spawning condition was inferred from the maturity of the ovaries. It was found that the coastal fish of each cohort exhibit at least two spawning periods per year which vary in length and time of occurrence from year to year. Fish taken from the offshore fishing grounds did not exhibit this variable spawning pattern. Although samples were not available for all months, the data showed that each cohort has a spawning period of at least 7 months and may spawn year around. Samples from offshore areas also had much higher percentages of spawners than those from the coastal areas. Temporal differences in spawning are not maintaining the genetically separate groups found in the fishery, since fish of both recruitment cohorts spawn at the same time. Also, fish of both the X and Y cohorts spawned in all areas examined; however, these data are insufficient to determine whether spatial isolation of spawning groups is occurring within the areas. SPANISH: Se examinó el desove del atún aleta amarilla (Thunnus albacares) en el Océano Pacífico oriental para averiguar la existencia de subpoblaciones separadas en esta zona. La investigación genética bioquímica del aleta amarilla indica que existen varios grupos genéticamente distintos en el Pacífico oriental. Además, el aleta amarilla pertenece a dos cohortes de reclutamiento X e Y, formadas por una mezcla de estos grupos genéticamente diferentes. Los datos del desove fueron obtenidos de 1956 a 1961, en las regiones neríticas de pesca y desde 1970 a 1973, en las áreas oceánicas de pesca. Se analizaron los aspectos temporales y espaciales del desove de los peces de las dos cohortes, para determinar si el comportamiento reproductor del aleta amarilla, apoya la existencia de subpoblaciones genéticamente diferentes. Se derivó la condición del desove según la madurez de los ovarios. Se encontró que los peces costeros de cada cohorte exhibían por lo menos dos períodos anuales de desove que varían en duración y fecha de ocurrencia de un año a otro. Los peces capturados en las regiones oceánicas de pesca no exhibieron este patrón variable de desove. Aunque o se consiguieron muestras en todos los meses, los datos indican que cada cohorte tiene un período de desove por lo menos de 7 meses y puede que desoven durante todo el año. Las muestras de las regiones oceánicas tuvieron porcentajes mucho mayores de reproductores que los de las zonas neríticas. Las diferencias temporales en el desove no sirven para explicar la presencia de grupos genéticamente separados que se encuentran en la pesca, ya que los peces de ambas cohortes de reclutamiento desovan al mismo tiempo. Además, los peces de ambas cohortes (X e Y) desovan en todas las zonas examinadas; sin embargo, estos datos no son suficientes para determinar si el aislamiento de los grupos de desove ocurre en las zonas. (PDF contains 53 pages.)

An evaluation of the effects of blue crab (Callinectes sapidus) behavior on the efficacy of crab pots as a tool for estimating population abundance

Crab traps have been used extensively in studies on the population dynamics of blue crabs to provide estimates of catch per unit of effort; however, these estimates have been determined without adequate consideration of escape rates. We examined the ability of the blue crab (Callinectes sapidus) to escape crab pots and the possibility that intraspecific crab interactions have an effect on catch rates. Approximately 85% of crabs that entered a pot escaped, and 83% of crabs escaped from the bait chamber (kitchen). Blue crabs exhibited few aggressive behavioral interactions in and around the crab pot and were documented to move freely in and out of the pot. Both the mean number and size of crabs caught were significantly smaller at deeper depths. Results from this study show that current estimates of catch per unit of effort may be biased given the high escape rate of blue crabs documented in this study. The results of this paper provide a mechanistic view of trap efficacy, and reveal crab behavior in and around commercial crab pots.

Sex-change rules, stock dynamics, and the performance of spawning-per-recruit measures in protogynous stocks

Predicting and under-standing the dynamics of a population requires knowledge of vital rates such as survival, growth, and reproduction. However, these variables are influenced by individual behavior, and when managing exploited populations, it is now generally realized that knowledge of a species’ behavior and life history strategies is required. However, predicting and understanding a response to novel conditions—such as increased fishing-induced mortality, changes in environmental conditions, or specific management strategies—also require knowing the endogenous or exogenous cues that induce phenotypic changes and knowing whether these behaviors and life history patterns are plastic. Although a wide variety of patterns of sex change have been observed in the wild, it is not known how the specific sex-change rule and cues that induce sex change affect stock dynamics. Using an individual based model, we examined the effect of the sex-change rule on the predicted stock dynamics, the effect of mating group size, and the performance of traditional spawning-per-recruit (SPR) measures in a protogynous stock. We considered four different patterns of sex change in which the probability of sex change is determined by 1) the absolute size of the individual, 2) the relative length of individuals at the mating site, 3) the frequency of smaller individuals at the mating site, and 4) expected reproductive success. All four pat-terns of sex change have distinct stock dynamics. Although each sex-change rule leads to the prediction that the stock will be sensitive to the size-selective fishing pattern and may crash if too many reproductive size classes are fished, the performance of traditional spawning-per-recruit measures, the fishing pattern that leads to the greatest yield, and the effect of mating group size all differ distinctly for the four sex-change rules. These results indicate that the management of individual species requires knowledge of whether sex change occurs, as well as an understanding of the endogenous or exogenous cues that induce sex change.

Feeding behavior and food preference of Penaeus monodon Fabricius with scrap tilapia

The time of day during which P. monodon feeds at different depth levels in earthen ponds, and its preference for three types of tilapia feeds (dry, fresh and fermented) were determined. It was observed that P. monodon concentrated at the bottom beds during the day and along the periphery of dikes during night-time, with a slight tendency to swim and feed towards the surface as darkness increased. P. monodon showed special preference for dried tilapia compared to fresh and fermented tilapia. P. monodon also showed adaptability to the platform method of feeding, especially during night-time.