Effects of seasonal change on activity rhythms and swimming behavior of age-0 bluefish (Pomatomus saltatrix) and a description of gliding behavior

Daily and seasonal activity rhythms, swimming speed, and modes of swimming were studied in a school of spring-spawned age-0 bluefish (Pomatomus saltatrix) for nine months in a 121-kL research aquarium. Temperature was lowered from 20° to 15°C, then returned to 20°C to match the seasonal cycle. The fish grew from a mean 198 mm to 320 mm (n= 67). Bluefish swam faster and in a more organized school during day (overall mean 47 cm/s) than at night (31 cm/s). Swimming speed declined in fall as temperature declined and accelerated in spring in response to change in photoperiod. Besides powered swimming, bluefish used a gliding-upswimming mode, which has not been previously described for this species. To glide, a bluefish rolled onto its side, ceased body and tail beating, and coasted diagonally downward. Bluefish glided in all months of the study, usually in the dark, and most intensely in winter. Energy savings while the fish is gliding and upswimming may be as much as 20% of the energy used in powered swimming. Additional savings accrue from increased lift due to the hydrofoil created by the horizontal body orientation and slightly concave shape. Energy-saving swimming would be advantageous during migration and overwintering.

Age validation of Dover sole (Microstomus pacificus) by means of bomb radiocarbon

We used bomb radiocarbon (14C) in this age validation study of Dover sole (Microstomus pacificus). The otoliths of Dover sole, a commercially important fish in the North Pacific, are difficult to age and ages derived from the current break-andburn method were not previously validated. The otoliths used in this study were chosen on the basis of estimated birth year and for the ease of interpreting growth zone patterns. Otolith cores, material representing years 0 through 3, were isolated and analyzed for 14C. Additionally, a small number of otoliths with difficult-to-interpret growth patterns were analyzed for 14C to help determine age interpretation. The measured Dover sole 14C values in easier-to-interpret otoliths were compared with a 14C reference chronology for Pacific halibut (Hippoglossus stenolepis) in the North Pacific. We used an objective statistical analysis where sums of squared residuals between otolith 14C values of Dover sole and the reference chronology were examined. Our statistical analysis also included a procedure where the Dover sole 14C values were standardized to the reference chronology. These procedures allowed an evaluation of aging error. The 14C results indicated that the Dover sole age estimates from the easier-to-interpret otoliths with the break-and-burn method are accurate. This study validated Dover sole ages from 8 to 47 years.

Age-specific movement patterns of sablefish (Anoplopoma fimbria) in Alaska

Over 34,000 age 0–2 juvenile sablefish (Anoplopoma fimbria) were tagged and released in southeast Alaska waters during 1985–2005. The data set resulting from this tagging study was unusual because of its time span (20 years) and because age could be reliably inferred from release length (i.e., tagged and released fish were of known age); thus, age-specific movement patterns could be examined. The depth- and area-related recovery patterns supported the concepts that sablefish move to deeper water with age and migrate counterclockwise in the Gulf of Alaska. Availability to the fishery increased rapidly for fish of younger ages, peaked at age 5 to 6, and then gradually declined as sablefish moved deeper with age. Decreased availability with age may occur because of lower fishing effort in deep water and could have substantial implications for sablef ish stock assessments because “domeshaped” availability influences the reliability of abundance estimates. The area-related recovery pattern was not affected by year-class strength; i.e., there was no significant densitydependent relationship.

Age- and length-at-maturity of female arrowtooth flounder (Atheresthes stomias) in the Gulf of Alaska

Arrowtooth flounder (Atheresthes stomias) has had the highest abundance of any groundfish species in the Gulf of Alaska since the 1970s (Matarese et al., 2003; Turnock et al., 2005; Blood et al., 2007); however, commercial catches have been restricted because Pacific halibut (Hippoglossus stenolepis) are caught as bycatch in the fishery. Arrowtooth flounder plays a key role in the ecosystem because it is a dominant organism within the food web, both as an apex predator of fish and invertebrates, as well as an important prey for walleye pollock (Theragra chalcogramma; Aydin et al., 2002). Walleye pollock is the dominant groundfish in the Bering Sea, a principal groundfish in the Gulf of Alaska, and the primary prey for marine mammals. The distribution of arrowtooth flounder extends from Cape Navarin and the eastern Sea of Okhotsk in Russia, across the Bering Sea, Aleutian Islands, Gulf of Alaska, and south to the coast of central California (Shuntov, 1964; Britt and Martin, 2001; Chetvergov, 2001; Weinberg et al., 2002; Zenger, 2004). Because of the importance of arrowtooth flounder in the marine ecosystem of A laska, a maturity study of this species was undertaken to determine age-at-maturity, which is essential for age-based stock management models. Before these results, management has had to rely upon a length-at-maturity-based estimate (Zimmermann, 1997) to manage stocks in the Gulf of Alaska (GOA), Bering Sea, and Aleutian Islands. The central GOA was selected as the location for this maturity study Age- and length-at-maturity of female arrowtooth flounder (Atheresthes stomias) in the Gulf of Alaska because it contains approximately 70% of the total Gulf of Alaska arrowtooth flounder biomass (1.9×106 t, age 3 and older)— the highest percentage in the world (Shuntov, 1964; Britt and Martin, 2001; Weinberg et al., 2002; Wilderbuer and Nichol, 2006).

Age, growth, and reproduction of dolphinfish (Coryphaena hippurus) caught off the coast of North Carolina

Age, growth, and reproductive data were obtained from dolphinfish (Coryphaena hippurus, size range: 89 to 1451 mm fork length [FL]) collected between May 2002 and May 2004 off North Carolina. Annual increments from scales (n=541) and daily increments from sagittal otoliths (n=107) were examined; estimated von Bertalanffy parameters were L∞ (asymptotic length)=1299 mm FL and k (growth coefficient)=1.08/yr. Daily growth increments reduced much of the residual error in length-at-age estimates for age-0 dolphinfish; the estimated average growth rate was 3.78 mm/day during the first six months. Size at 50% maturity was slightly smaller for female (460 mm FL) than male (475 mm FL) dolphinfish. Based on monthly length-adjusted gonad weights, peak spawning occurs from April through July off North Carolina; back-calculated hatching dates from age-0 dolphinfish and prior reproductive studies on the east coast of Florida indicate that dolphinfish spawning occurs year round off the U.S. east coast and highest levels range from January through June. No major changes in length-at-age or size-at-maturity have occurred since the early 1960s, even after substantial increases in fishery landings.

Incorporating fishery observer data into an integrated catch-at-age and multiyear tagging model for estimating mortality rates and abundance

Tagging experiments are a useful tool in fisheries for estimating mortality rates and abundance of fish. Unfortunately, nonreporting of recovered tags is a common problem in commercial fisheries which, if unaccounted for, can render these estimates meaningless. Observers are often employed to monitor a portion of the catches as a means of estimating reporting rates. In our study, observer data were incorporated into an integrated model for multiyear tagging and catch data to provide joint estimates of mortality rates (natural and f ishing), abundance, and reporting rates. Simulations were used to explore model performance under a range of scenarios (e.g., different parameter values, parameter constraints, and numbers of release and recapture years). Overall, results indicated that all parameters can be estimated with reasonable accuracy, but that fishing mortality, reporting rates, and abundance can be estimated with much higher precision than natural mortality. An example of how the model can be applied to provide guidance on experimental design for a large-scale tagging study is presented. Such guidance can contribute to the successful and cost-effective management of tagging programs for commercial fisheries.

Age and growth of swordfish (Xiphias gladius) caught by the Hawaii-based pelagic longline fishery

We verified the age and growth of swordfish (Xiphias gla-dius) by comparing ages determined from annuli in fin ray sections with daily growth increments in otoliths. Growth of swordfish of exploitable sizes is described on the basis of annuli present in cross sections of the second ray of the first anal fins of 1292 specimens (60−260 cm eye-to-fork length, EFL) caught in the region of the Hawaii-based pelagic longline fishery. The position of the initial fin ray annulus of swordfish was verified for the first time with the use of scanning electron micrographs of presumed daily growth increments present in the otoliths of juveniles. Fish growth through age 7 was validated by marginal increment analysis. Faster growth of females was confirmed, and the standard von Bertalanffy growth model was identified as the most parsimonious for describing growth in length for fish greater than 60 cm EFL. The observed growth of three fish, a year-old in size when first caught and then recaptured from 364 to1490 days later, is consistent with modeled growth for fish of this size range. Our novel approach to verifying age and growth should increase confidence in conducting an age-structured stock assessment for swordfish in the North Pacific Ocean.

Age composition and distribution of red drum (Sciaenops ocellatus) in offshore waters of the north central Gulf of Mexico: an evaluation of a stock under a federal harvest moratorium

Because of a lack of fishery-dependent data, assessment of the recovery of fish stocks that undergo the most aggressive form of management, namely harvest moratoriums, remains a challenge. Large schools of red drum (Sciaenops ocellatus) were common along the northern Gulf of Mexico until the late 1980s when increased fishing effort quickly depleted the stock. After 24 years of harvest moratorium on red drum in federal waters, the stock is in need of reassessment; however, fisherydependent data are not available in federal waters and fishery-independent data are limited. We document the distribution, age composition, growth, and condition of red drum in coastal waters of the north central Gulf of Mexico, using data collected from a nearshore, randomized, bottom longline survey. Age composition of the fishery-independent catch indicates low mortality of fish age 6 and above and confirms the effectiveness of the federal fishing moratorium. Bottom longline surveys may be a cost-effective method for developing fishery-independent indices for red drum provided additional effort can be added to nearshore waters (<20 m depth). As with most stocks under harvest bans, effective monitoring of the recovery of red drum will require the development of fishery-independent indices. With limited economic incentive to evaluate non-exploited stocks, the most cost-effective approach to developing such monitoring is expansion of existing fishery independent surveys. We examine this possibility for red drum in the Gulf of Mexico and recommend the bottom longline survey conducted by the National Marine Fisheries Service expand effort in nearshore areas to allow for the development of long-term abundance indices for red drum.

Parameterizing probabilities for estimating age-composition distributions for mixture models

When estimating parameters that constitute a discrete probability distribution {pj}, it is difficult to determine how constraints should be made to guarantee that the estimated parameters { pˆj} constitute a probability distribution (i.e., pˆj>0, Σ pˆj =1). For age distributions estimated from mixtures of length-at-age distributions, the EM (expectationmaximization) algorithm (Hasselblad, 1966; Hoenig and Heisey, 1987; Kimura and Chikuni, 1987), restricted least squares (Clark, 1981), and weak quasisolutions (Troynikov, 2004) have all been used. Each of these methods appears to guarantee that the estimated distribution will be a true probability distribution with all categories greater than or equal to zero and with individual probabilities that sum to one. In addition, all these methods appear to provide a theoretical basis for solutions that will be either maximum-likelihood estimates or at least convergent to a probability distribut

A comparison of length-related and age-related growth parameters of newaiby Otolithes ruber in Kuwait waters

The growth parameters of Otolithes ruber (Sciaenidae) were determined from both length-frequency and length-at-age data collected from Kuwait waters from 1984 to 1986. The similarity of the growth parameters is reflected in the small range of the parameters o' (=log sub(10)K+2logL) which indicates the compatibility of the two methods for this relatively short-lived species.

Using eye lens diameter as age indicator of young Lithognathus mormyrus and Diplodus vulgaris

Eye lens diameter was analyzed in two sparid fish species, Lithognathus mormyrus and Diplodus vulgaris, in order to determine the possibility of using these data for age determination. The results showed that the technique could be adopted for determining the age of the two species when the specimens are very young. The method is especially useful for age determination when otolith or scale rings are not visible or when false rings may give erroneous readings.

Can the age of the tropical species be determined by otolith measurement?: a study using Pristipomoides filamentosus (Pisces: Lutjanidae) from the Mahe Plateau, Seychelles

The sagittal otoliths of bluespot jobfish (Pristipomoides flamentosus) from the Mahe Plateau, Seychelles, were examined for growth rings using light microscopy. Banding with putative annual and monthly frequency were observed. Consistent age estimates were derived from each of the two patterns. The resulting length-at-age data were use t estimate the parameters K and t sub(0), viz: K=0.33, t sub(0) = 0.16 for males and K = 0.36, t sub(0) = 0.06 for females (using von Bertalanffy plots). Possible causes of the banding are discussed.

Age determination in tropical fish

This essay presents evidence that check marks on the hard parts of tropical fishes can be used for aging these, in spite of the small seasonal temperature and other environmental oscillations prevailing in the tropics. The ideas presented in this article were over 50 years ahead of their time.

Age and growth of three species of Lake Victoria fish determined by means of otolith daily growth rings

The sagittal otoliths of Lates niloticus, Haplochromis obesus, and Oreochromis niloticus from Lake Victoria were examined for daily growth rings using scanning electron microscopy. In the three species the increments were clear and thick enough to allow future studies with light microscopy. The daily nature of the increments seems supported by the rhythmic growth that were found.

Age- or length-based methods of growth estimation. What drives the choice?

Based upon a global comparison of over 400 fisheries, the Principal Components Analysis (PCA) methodology was used to identify factors affecting the choice of growth estimation methods. Of the six factors examined, the growth rate (K) and asymptotic length (L8) explained most of the variations. Financial resources, i.e., Gross National Product (GNP), and latitude were also important factors.