Growth of long-finned squid, Loligo peali, in the northwest Atlantic

The application of statolith ageing techniques to long-fined squid, Loligo pealei, suggests that this species has a life span of less than one year and grows more rapidly than preiously thought. In this study we provide direct estimates of growth for long-finned squid in the northwest Atlantic based on a data set of 353 animals aged by counting putative daily statolith increments. We examine empirical patterns in length and weigth at age and estimate parameters of a general growth model. The results indicate that growth rate increases rapidly as squid age and that growth in length and weight is expotential. Although there is substantial heterogeity in L. pealei size at age, sexual dimorphism is evident: males grow more rapidly than do females and achieve lager sizes. Back-calculated hatching dates show that L. pealei spawning is not restricted to spring through late-autumn, as previously supposed, but occurs durin winter months as well. Differences between growth rates of squid hatched during June-October and November-May are suggested and lend support to the hypothesis that growth can be influened by seasonal environmental condititions. We discuss the practical impilcations of our findings for the assessment and management of the long-finned squid stock in the northwest Atlantic

Effects of zooplankton size and concentration and light intensity on the feeding behavior of Atlantic mackerel \u3cem\u3eScomber scombrus\u3c/em\u3e

Atlantic mackerel Scomber scombrus had low clearance rates when fed older stage copepodites of the copepod Calanus finmarchicus at high concentrations and high clearance rates at low concentrations. These rates were consistent with filter feeding at high concentrations and particulate feeding at low concentrations. Intermediate and small copepods presented together at high concentrations were cleared at lower rates than the large C. finmarchicus, suggesting lower filtration efficiencies. Intermediate and small copepods were presented over a range of light intensities (8.2 x 10-8 to 1.6 x 100 µE m-2 s-1). Feeding rate did not change significantly between 1.6 x 100 and 2.0 x 10-6 µE m-2 s-1, but decreased to nearly zero at 8.2 x 10-8 µE m-2 s-1, indicating a light intensity threshold for feeding of about 10-7 µE m-2 s-1. This threshold enables mackerel to feed throughout the night near the ocean surface. Swimming speed decreased to a lesser degree than feeding rate at the lowest light intensity, indicating that the change in filter-feeding rate is only partially due to the change in speed. The school dispersed in both low and high light levels, but spacing between fish did not appear to be related to feeding rate

FEEDING PATTERNS OF THE LONG-FINNED SQUID, LOLIGO PEALEI, IN NEW ENGLAND WATERS

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Development and application of an objective method for classifying long-finned squid, Loligo pealei, into sexual maturity stages

An objective method of classifying long-finned squid, £Oligo pealei, by their sexual maturity was developed using cluster and discriminant analysis techniques. The resulting system recognizes four developmental,stages and employs a maximum,of only five easily measured,morphometric,parame­ ters. Such a system is easy to use and is suitable for large-scale field studies with relatively untrained help. The value of determining,clearly recognized reproductive stages is demonstrated,by an appli­ cation of the method

Validation of a semi-automatic image analysis system to age squids and its application to age Illex coindetii statoliths

10 pages, 3 figures, 3 tables.The validity of a semi-automatic image analysis system employing digital image enhancement was demonstrated by re-analysing a set of previously analysed, known-age Sepioteuthis lessoniana statoliths. Linear regression models using both the manual and semi-automatic growth increment counts successfully predicted the true age of the test statoliths to a high degree of accuracy and precision and fully supported the one increment per day hypothesis. Thus this set of known age statoliths served as a reference standard for the counting method. After "calibrating" the semi-automatic image analysis system with the reference standards the method was then used to determine the ages of a large (n=312) set of Illex coindetii statoliths of unknown age. The results of this analysis were less clear than the S. lessoniana analysis. The semi-automatic counts predicted mantle lengths (ML) more precisely than did the manual counts. Significant differences were found between the two counting methods. For the Illex data set, the linear model to estimate ML from putative age predicted negative y-intercept values for both sexes and counting methods. Thus a power function model was selected as the more biologically meaningful predictor of ML. The accuracy of the I. coindetii analysis cannot be determined as the daily increment hypothesis remains to be verified for this species.This research was partly supported by NOAA, NMFS (USA) Grant #NA 36 RG0503 to W. K. Macy of the University of Rhode Island Sea Grant Program and by a fellowship to A. F. González from the Spanish Ministry of Education and Science.Peer reviewe

Metabolic rate in relation to temperature and swimming speed, and the cost of filter feeding in Atlantic menhaden, Brevoortia tyrannus

Respiration rates of nonfeeding adult menhaden induced to swim against currents of various speeds in a large circular flume at 10°, 15°, and 20°C were measured in order to quantify the cost of swimming separately from total metabolic expenditure during filter feeding. Standard metabolic rates of 0.040, 0.073, and 0.087 mg O2/(g wet wt. h) at 10°C, 15°C, and 20°C were estimated by extrapolation of the relationship of swimming speed and metabolic rate to zero swimming speed. We determined that when menhaden filter-feed at 20°C, at the preferred swimming speed of 41.3 cm/s, filtering and specific dynamic action (SDA) account for 59% of total energetic expenditures. The cost of locomotion was only about 23% of the total expenditure. Our results are compared with routine oxygen consumption rates of larval and juvenile menhaden as a function of temperature and with extensive metabolic data for sockeye salmon

Validation of a semi-automatic image analysis system to age squids and its application to ageIllex coindetiistatoliths

The validity of a semi-automatic image analysis system employing digital image enhancement was demonstrated by re-analysing a set of previously analysed, known-age Sepioteuthis lessoniana statoliths. Linear regression models using both the manual and semi-automatic growth increment counts successfully predicted the true age of the test statoliths to a high degree of accuracy and precision and fully supported the one increment per day hypothesis. Thus this set of known age statoliths served as a reference standard for the counting method. After “calibrating” the semi-automatic image analysis system with the reference standards the method was then used to determine the ages of a large (n=312) set of Illex coindetii statoliths of unknown age. The results of this analysis were less clear than the S. lessoniana analysis. The semi-automatic counts predicted mantle lengths (ML) more precisely than did the manual counts. Significant differences were found between the two counting methods. For the Illex data set, the linear model to estimate ML from putative age predicted negative y-intercept values for both sexes and counting methods. Thus a power function model was selected as the more biologically meaningful predictor of ML. The accuracy of the I. coindetii analysis cannot be determined as the daily increment hypothesis remains to be verified for this species