Comparison of electrofishing and trammel netting variability for sampling native fishes

The variability in size structure and relative abundance (CPUE; number of fish ≥200 mm total length, L_T, collected per hour of electrofishing or trammel netting) of three native Colorado River fishes, the endangered humpback chub Gila cypha, flannelmouth sucker Catostomus latipinnus and bluehead sucker Catostomus discobolus, collected from electrofishing and trammel nets was assessed to determine which gear was most appropriate to detect trends in relative abundance of adult fishes. Coefficient of variation (CV) of CPUE ranged from 210 to 566 for electrofishing and 128 to 575 for trammel netting, depending on season, diel period and species. Mean CV was lowest for trammel nets for humpback chub (P = 0·004) and tended to be lower for flannelmouth sucker (P = 0·12), regardless of season or diel period. Only one bluehead sucker >200 mm was collected with electrofishing. Electrofishing and trammel netting CPUE were not related for humpback chub (r = ?0·32, P = 0·43) or flannelmouth sucker (r = ?0·27, P = 0·46) in samples from the same date, location and hour set. Electrofishing collected a higher proportion of smaller (<200 mm L_T) humpback chub (P < 0·001), flannelmouth suckers (P < 0·001) and bluehead suckers (P < 0·001) than trammel netting, suggesting that conclusions derived from one gear may not be the same as from the other gear. This is probably because these gears fished different habitats, which are occupied by different fish life stages. To detect a 25% change in CPUE at a power of 0·9, at least 473 trammel net sets or 1918 electrofishing samples would be needed in this 8 km reach. This unattainable amount of samples for both trammel netting and electrofishing indicates that detecting annual changes in CPUE may not be practical and analysis of long‐term data or stock assessment models using mark‐recapture methods may be needed to assess trends in abundance of Colorado River native fishes, and probably other rare fishes as well.     

Reproductive biology of the guitarfish Rhinobatos percellens (Chondrichthyes,Rhinobatidae) from the São Paulo Coast,Brazil, western South Atlantic Ocean

The reproductive biology of the guitarfish Rhinobatos percellens was studied from 751 specimens caught by bottom pair trawlers off the coast of São Paulo, Brazil, between c. 24° 00′ S; 45° 15′ W and c. 25° 10′ S; 47° 52′ W, from September 2007 to August 2009. The total length (L_T) and total mass (M_T) relationship for males and females combined was M_T = 1·29E‐06 L_T^3·15 (r = 0·99, n = 751). The mean L_T of sexually mature specimens was 548 mm for males and 583 mm for females. Clasper growth was allometric and showed three distinct phases. Most claspers were calcified in specimens of c. 550 mm L_T. The mean diameter of the largest oocyte was 29·8 mm, the mean ovarian fecundity was seven oocytes and ovulation occurred between August and November. Uterine fecundity ranged from two to 13 embryos (mean of five embryos). Larger females had higher litter sizes and larger embryos; the size‐at‐birth was c. 200 mm L_T. The hepato‐somatic index oscillated seasonally for males and females; the gonado‐somatic index had little variation in males, but varied seasonally in females. The presence of many non‐pregnant adult females and of encapsulated eggs during two consecutive seasons suggests a resting period between gestations and the possibility of diapause.     

Population biology of an endangered species: the common guitarfish Rhinobatos rhinobatos in Lebanese marine waters of the eastern Mediterranean Sea

This study focuses on the population biology of the common guitarfish Rhinobatos rhinobatos, a cartilaginous fish listed as Endangered in the International Union for the Conservation of Nature (IUCN) Red List. Between December 2012 and January 2014, 67 individuals were collected by bottom longlining in coastal Lebanese marine waters at different ports at depths ranging from 10 to 110 m. The total length (L_T) of the specimens ranged from 50 to 143 cm, and the mean ± s.d . was 76·2 ± 19·7 cm. The most common L_T classes were between 60 and 70 cm. The total mass of the specimens ranged from 410 to 10 000 g, and the mean ± s.d . was 1841 ± 1987 g. A total of 34 males and 33 females were collected, and the sex ratio was not significantly different from 1:1. The mass and L_T relationship showed positive allometric growth (b = 3·096 and r² = 0·99), and the mean ± s.d . L_T at which 50% of the individuals were sexually mature was 84·73 ± 5·81 cm for females and 78·57 ± 4·88 cm for males. The gonado‐somatic and hepato‐somatic indices were determined along with a condition factor, and parturition appeared to occur in winter. The primary prey items found in the fish stomachs during the autumn and winter seasons were Penaeidae. The results of this study will help to parameterize models of the population dynamics for this exploited fish stock to ensure the long‐term sustainability of its fishery.     

Trophic size‐structure of sailfish Istiophorus platypterus in eastern Taiwan estimated by stable isotope analysis

To examine trophic dynamics over different size classes, an isotopic study of sailfish Istiophorus platypterus life‐history stages was carried out. Samples were collected from eastern Taiwan and the South China Sea during April 2009 and February 2012. A total of 263 samples (111–245 cm, lower jaw fork length, L_LJFL) were examined for changes in trophic structure in relation to L_LJFL by using stable isotope analysis of carbon (δ¹³C) and nitrogen (δ¹⁵N). The δ¹⁵N values for I. platypterus ranged from 7·51 to 14·19‰ (mean ± s.d . = 12·06 ± 1·16‰) and the δ¹³C values ranged from ?22·04 to ?15·48‰ (mean ± s.d . = ?17·62 ± 1·10‰). The δ¹⁵N values were positively dependent on L_LJFL (r² = 0·377), whereas δ¹³C were negatively dependent on L_LJFL (r² = 0·063). There were significantly different seasonal changes in nitrogen and carbon isotopic concentration, but no significant differences in concentrations between eastern Taiwan and the South China Sea were reported. The trophic level (T_L) of each L_LJFL class was correlated, starting from 2·84 T_L for size class I (L_LJFL < 140 cm) and reaching 5·03 T_L for size class VI (L_LJFL > 221 cm). The mean ± s.d . T_L was 4·43 ± 0·19 for all samples. The results reveal that I. platypterus occupies a wide range of trophic levels and different size classes occupy different trophic positions in the pelagic ecosystem.     

Diet and feeding behaviour of longnosed skate Dipturus oxyrinchus

A total of 255 longnosed skate Dipturus oxyrinchus caught in Sardinian waters (central‐western Mediterranean Sea), was analysed with respect to fish total length (L_T), season and depth, in order to provide information on diet and feeding behaviour. Specimens ranging from 93 to 1153 mm L_T, were collected at depths between 121 and 671 m, during experimental trawl surveys carried out from 2005 to 2010. The diet comprised crustaceans [prey specific index of relative importance (%I_PSRI) = 72·69], teleosts (%I_PSRI = 10·28) and molluscs (%I_PSRI = 10·94). Levins' index (B_i) showed a narrow niche breadth (B_i = 0·35). The mean ± s.e. trophic level (T_L) was 3·63 ± 0·50. The analysis showed major ontogenetic changes in the feeding behaviour. Early life stages were characterized by a benthic diet, which changed to benthopelagic during growth. Mysids, particularly Lophogaster typicus (%I_PSRI = 34·51), were the main prey items of immature individuals, replaced by euphausiids, mainly Meganyctiphanes norvegica (%I_PSRI = 13·19), in maturing fish. Crustaceans became less important in mature specimens, being replaced by molluscs (%I_PSRI = 28·99) and teleosts (%I_PSRI = 24·56). A concomitant increase of the T_L was recorded (mean ± s.e. = 3·41 ± 0·44, 3·75 ± 0·54 and 4·28 ± 0·61 for immature, maturing and mature individuals). These feeding patterns ensured low levels of intraspecific competition. This study provides new information about the role that the D. oxyrinchus plays in the marine food chain and data now essential to formulate new and effective management plans for this species.     

Interaction between migration behaviour and estuarine mortality in cultivated Atlantic salmon Salmo salar smolts

Migration behaviour and estuarine mortality of cultivated Atlantic salmon Salmo salar smolts in a 16 km long estuary were studied using two methods: (1) acoustic telemetry and (2) group tagging in combination with trap nets. Progression rates of surviving individuals through the estuary were relatively slow using both methods [0·38 L_T (total length) s^?1 v. 0·25 L_T s^?1]. In 2012, the progression rate was slow from the river to the estuary (0·55 L_T s^?1) and the first part of the estuary (0·31 L_T s^?1), but increased thereafter (1·45–2·21 L_T s^?1). In 2013, the progression rate was fast from the river to the estuary (4·31 L_T s^?1) but was slower thereafter (0·18–0·91 L_T s^?1). Survival to the fjord was higher in 2012 (47%) compared to 2013 (6%). Fast moving individuals were more likely to migrate successfully through the estuary compared to slower moving individuals. Adult recapture of coded‐wire‐tagged S. salar was generally low (0·00–0·04%). Mortality hot spots were related to topographically distinct areas such as the river outlet (in 2012) or the sill separating the estuary and the fjord (in 2013). At the sill, an aggregation of cod Gadus morhua predating on cultivated smolts was identified. The results indicate that slow progression rates through the estuary decreases the likelihood of smolts being detected outside the estuary. The highly stochastic and site‐specific mortality patterns observed in this study highlight the complexity in extrapolating mortality patterns of single release groups to the entire smolt run of wild S. salar.     

Life history characteristics of an invasive cyprinid fish (Carassius gibelio) in Chimaditis Lake (northern Greece)

The life history characteristics of an invasive cyprinid fish, the Prussian carp (Carassius gibelio) were examined in Lake Chimaditis (northern Greece). The population is dominated by females that are able to reproduce gynogenetically. Fish samples were collected using trammel nets from August 2004 to July 2005. Their total length (TL) ranged between 21.9 and 37.0 cm. The length–weight relationship was W = 0.0336TL^2.81 (r² = 0.92, n = 600) and the mean Fulton condition factor exhibited monthly variation from 0.172 (May) to 0.186 (August). According to the annual growth marks present, the lifespan of the Prussian carp in Lake Chimaditis is 6 years. The growth parameters were estimated as L_∞ = 34.46 cm, K = 0.297 year^?1, t₀ = ?1.994 year. Absolute fecundity (F_A) ranged between 26 000 and 176 600 oocytes (mean = 66990) and relative fecundity between 78 and 251 oocytes per gram of total weight (mean = 158). Absolute fecundity increased exponentially with length (F_A = 0.286 × TL^3.66, r² = 0.66) and weight (F_A = 17.93 × W^1.36, r² = 0.73) of the fish.     

Catch composition,reproductive biology and diet of the bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae) from the south‐eastern Arabian Sea

Fishery and biological data are presented for the poorly known bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae), from the deep waters of the south‐eastern Arabian Sea. A total of 5318 individuals from by‐catch landings of deep‐water bottom set longlines, gillnets and shrimp trawl fisheries operating at depths of 200–1200 m were recorded between January 2008 and December 2011 at the Kochi Fisheries Harbour (Kerala). A total of 431 individuals, from 46 to 318 cm total length (L_T) and 0·8 to 132 kg total mass (M_T), were examined to determine biological data for this species. The L_T at which 50% were mature (L_T50) for females and males was estimated at 189 and 187 cm L_T. Litter size ranged from 10 to 36 and size at birth was between 42 and 46 cm L_T. Dietary analysis of stomach contents revealed E. brucus feeds on a variety of prey including crustaceans (69% index of relative importance, I_RI), teleosts (25·8% I_RI), cephalopods (1·7% I_RI) and elasmobranchs (0·7% I_RI). This study provides the first detailed biological data for this species and also highlights the extent of the by‐catch fishery for this species in Indian waters.     

Age, growth, and sexual maturity of the yellownose skate Dipturus chilensis in the south‐eastern Pacific

The age and growth parameters of Dipturus chilensis were estimated by counting growth rings from thin sections of vertebral centra from 400 fish (246 females and 154 males), ranging from 23 to 124 cm total length (L_T), and backcalculating fish lengths at previous ages. Marginal increment analysis lent support to the hypothesis of annual deposition of band‐pairs, which formed during the winter months. The oldest female D. chilensis aged in this study was 21 years and 117 cm L_T, whereas the oldest male was 18 years and 93 cm L_T. A 4·7% index of average per cent error (I_APE) suggested that this is a precise method for calculating the age of D. chilensis. Observed L_T were lower than backcalculated L_T, which implies the influence of Lee's phenomenon. The von Bertalanffy growth equations, based on mean length‐at‐age data, were estimated as L_t = 128·3 (1 ? e^{?0·112 (t + 0·514)}) for females and L_t = 107·8 (1 ? e^{?0·134 (t + 0·862)}) for males where t is age (years). Growth was significantly different between sexes: females reached a larger adult size. Ages and lengths at 50% maturity were estimated at 14 years of age and 106 cm L_T for females and 11 years of age and 86 cm L_T for males. At c. 14 years, there was a decline in growth rates in females. The factor most likely responsible for this was sexual maturity, which caused a discontinuity in growth of female fish. These results show that this species is slow‐growing, long‐lived, relatively large and of delayed maturity, characteristics that make it vulnerable to exploitation.     

Diel vertical migrations of bathypelagic perch fry

The behaviour of young‐of‐the‐year (YOY) perch Perca fluviatilis as a dominant species in the assemblage of fry in the pelagic of Slapy Reservoir (Czech Republic), was studied during late May and mid‐June 2002 using acoustic methods and complementary net catches. During the day, perch fry were present simultaneously in littoral, epipelagic and bathypelagic habitats. Bathypelagic perch fry, forming a scattering layer, migrated vertically each day between the epilimnion and hypolimnion, with an amplitude of 11·0 m in May and 12·5 m in June. At dusk, the migratory bathypelagic fry mixed in the epilimnion with non‐migrating epipelagic fry and spent the night close to the thermocline (abundance maximum at 3–4 m in May, 0–2 m in June). In June, shoaling behaviour by some of the bathypelagic perch fry was also observed: the shoaling fry remained higher in the water column than the non‐shoaling fry. Both depths of the scattering layer and the depths of the fry shoals were strongly controlled by the light intensity. The contribution of the bathypelagic part of the population to the total numbers of pelagic perch fry decreased from 28·1% in May to 4·7% in June, while the density of all pelagic perch fry increased (c. 96 000 individuals ha^?1 in May and 142 000 individuals ha^?1 in June). In May, the bathypelagic (average total length, L_T, 11·9 mm) and epipelagic (average L_T 14·6 mm) perch fry differed in size while, in June, the epipelagic fry were divided into two distinct size groups. The more abundant group, of small epipelagic perch fry (average L_T 14·6 mm), was similar in size to the bathypelagic fry (average L_T 14·6 mm) while the less abundant group, of larger epipelagic fry (average L_T 34·4 mm), was similar in size to littoral perch fry (average L_T 35·0 mm). The results suggest that in perch fry three different survival strategies with different risks can be used in the same locality, time and year.     

Size and growth rate differences of larval Baltic sprat Sprattus sprattus collected with bongo and MIK nets

The effect of sampling with bongo (0·6 m diameter frame with 500 µm mesh) and Methot Isaac Kidd (MIK) (2 m diameter frame with 2 mm mesh finished with 500 µm codend) nets on standard length (L_S) range and growth rate differences was tested for larval Sprattus sprattus (n = 906, L_S range: 7·0–34·5 mm) collected during four cruises in the summer months of 2006, 2007, 2009 and 2010 in the southern Baltic Sea. Although the minimum size of larvae collected with the bongo and MIK nets was similar in each cruise (from c. 7 to 9 mm), the MIK nets permitted collecting larger specimens (up to c. 34 mm) than the bongo nets did (up to c. 27 mm). The growth rates of larvae collected with the bongo and MIK nets (specimens of the same size range were compared for three cruises) were not statistically different (mean = 0·55 mm day^?1, n = 788, L_S range: 7·0–27·4 mm), which means the material collected with these two nets can be combined and growth rate results between them were compared.     

Life‐history characteristics of the endangered Aristotle’s catfish (Silurus aristotelis Garman, 1890), Lake Pamvotis,north‐western Greece

The life history characteristics of Aristotle’s catfish, Silurus aristotelis (Agassiz 1856) were studied in Lake Pamvotis (northwestern Greece). Samples were collected on a monthly basis using gillnets, trammel‐nets and traps. Total lengths ranged from 11.1 to 36.7 cm. Sex ratio was biased toward females (F : M = 1.8 : 1) and was statistically different from unity (χ² = 46.94, P < 0.001). Spawning is from April to June. The relationship between total length and total weight showed positive allometric growth for males (TW = 0.0035 × TL^3.21, r² = 0.93, n = 198, P < 0.001) and females (TW = 0.0066 × TL^3.02, r² = 0.95, n = 363, P < 0.001). Age was determined on the annual growth marks formed on the spine of the pectoral fin. Based on cross‐section readings of the spine, lifespan of the Aristotle’s catfish was 5 years. Age classes 1 and 2 dominated the catches (39.1 and 40.0% of the total sample, respectively). Back‐calculated lengths at age showed a rapid increase in fish size during the first year of life, reaching 61.1% of maximum attainable length, and a declining growth rate thereafter. Growth parameters were calculated as L_∞ = 36.12 cm, K = 0.37 year^?1, t₀ = ?0.76 year based on the observed lengths at age and as L_∞ = 28.19 cm, K = 0.53 year^?1, t₀ = ?0.62 year based on the back‐calculated lengths at age. It seems that some of the life history traits (longevity, growth pattern, reproductive period) are influenced significantly by adverse effects of pollution and eutrophication on the lacustrine ecosystem.     

Age estimation of juvenile European hake Merluccius merluccius based on otolith microstructure analysis: a slow or fast growth pattern?

The main goal of this study was to examine otolith microstructure and to estimate the age and growth of European hake Merluccius merluccius from the eastern Mediterranean Sea. One hundred and twenty‐nine specimens ranging from 102 to 438 mm in total length (L_T) were used. Age estimations were based on the study of the otolith microstructure, which was revealed after grinding both frontal sides of otoliths. The enumerations of the daily growth increments (DGI) as well as their width (W_DGI) measurements were made on calibrated digital images. The number of DGI in otoliths ranged between 163 and 717. Four phases in the W_DGI evolution were distinguished: (1) larval–juvenile pelagic phase, with an increasing trend in W_DGI up to the 60th DGI, (2) settlement phase, with a short‐term deceleration in W_DGI between the 61st and 150th DGI, (3) juvenile demersal phase, characterized by a stabilization of W_DGI from 151st to 400th DGI and (4) adult phase, with a decreasing trend in W_DGI after the 400th DGI. Age, sex and month of formation were found to affect the W_DGI in all phases, with the exception of age at the juvenile demersal phase. The power curve with intercept model described best the relationship of M. merluccius L_T with age (T_DGI), according to Akaike criteria, revealing differences in growth between females [L_T = 65 · 36(T_DGI)^{0 · 40} ? 388 · 55] and males [L_T = 69 · 32(T_DGI)^{0 · 37} ? 352 · 88] for the sizes examined. The mean daily growth rates were 0·61 mm day^?1 for females and 0·52 mm day^?1 for males, resulting in an L_T of 283 and 265 mm at the end of their first year of life. In comparison with previous studies on the Mediterranean Sea, the results of this study showed a greater growth rate, similar to results from tagging experiments and otolith microstructure analyses for M. merluccius in other geographic areas.     

Slow growth of the overexploited milk shark Rhizoprionodon acutus affects its sustainability in West Africa

Age and growth of Rhizoprionodon acutus were estimated from vertebrae age bands. From December 2009 to November 2010, 423 R. acutus between 37 and 112 cm total length (L_T) were sampled along the Senegalese coast. Marginal increment ratio was used to check annual band deposition. Three growth models were adjusted to the length at age and compared using Akaike's information criterion. The Gompertz growth model with estimated size at birth appeared to be the best and resulted in growth parameters of L_∞ = 139·55 (L_T) and K = 0·17 year^?1 for females and L_∞ = 126·52 (L_T) and K = 0·18 year^?1 for males. The largest female and male examined were 8 and 9 years old, but the majority was between 1 and 3 years old. Ages at maturity estimated were 5·8 and 4·8 years for females and males, respectively. These results suggest that R. acutus is a slow‐growing species, which render the species particularly vulnerable to heavy fishery exploitation. The growth parameters estimated in this study are crucial for stock assessments and for demographic analyses to evaluate the sustainability of commercial harvests.     

Life‐history strategies of the rock hind grouper Epinephelus adscensionis at Ascension Island

Epinephelus adscensionis sampled from Ascension Island, South Atlantic Ocean, exhibits distinct life‐history traits, including larger maximum size and size at sexual maturity than previous studies have demonstrated for this species in other locations. Otolith analysis yielded a maximum estimated age of 25 years, with calculated von Bertalanffy growth parameters of: L_∞ = 55·14, K = 0·19, t₀ = ?0·88. Monthly gonad staging and analysis of gonad‐somatic index (I_G) provide evidence for spawning from July to November with an I_G peak in August (austral winter), during which time somatic growth is also suppressed. Observed patterns of sexual development were supportive of protogyny, although further work is needed to confirm this. Mean size at sexual maturity for females was 28·9 cm total length (L_T; 95% C.I. 27·1–30·7 cm) and no females were found >12 years and 48·0 cm L_T, whereas all confirmed males sampled were mature, >35·1 cm L_T with an age range from 3 to 18 years. The modelled size at which 50% of individuals were male was 41·8 cm (95% C.I. 40·4–43·2 cm). As far as is known, this study represents the first comprehensive investigation into the growth and reproduction of E. adscensionis at its type locality of Ascension Island and suggests that the population may be affected less by fisheries than elsewhere in its range. Nevertheless, improved regulation of the recreational fishery and sustained monitoring of abundance, length frequencies and life‐history parameters are needed to inform long‐term management measures, which could include the creation of marine reserves, size or temporal catch limits and stricter export controls.     

Dietary analysis of the herbivorous hemiramphid Hyporhamphus regularis ardelio: an isotopic approach

The stable isotope values for a range of size classes of Hyporhamphus regularis ardelio from Moreton Bay, south‐east Australia were determined. There was a positive linear relationship between δ¹³C and standard length (L_S)(δ¹³C = 0·034 L_S ? 16·23; r² = 0·78). δ¹³C ranged from ?8·48 to ?17·29‰ with the smallest size class (50 mm L_S) being on average 1·04‰ enriched with respect to that of zooplankton (Temora turbinata) and 7·97‰ depleted compared to Zostera capricorni. δ¹³C was positively correlated with L_S(P < 0·01)(more enriched with increasing L_S) with those fish of the largest size class (225 mm L_S) being 9·86 and 0·84‰ enriched than T. turbinata and Z. capricorni, respectively. There was no detectable trend in δ¹⁵N values with L_S(P > 0·01) with δ¹⁵N, ranging from 9·18 to 11·00‰. Fish of all size classes were on average 2·32 and 7·63‰ more enriched than zooplankton and seagrass, respectively. Carbon isotope data indicate that H. r. ardelio commence life as carnivores and change to a diet in which seagrass is the primary carbon source. The dependence on animal matter, however, is always present. Due to the low percentage of nitrogen in Z. capricorni(2·5%) compared to zooplankton (9·1%) it appears that nitrogen from zooplankton is necessary throughout their life history with the carbon requirements for these fish coming chiefly from Z. capricorni.     

Hypoxia tolerance decreases with body size in red drum Sciaenops ocellatus

Mass‐specific oxygen consumption rate, i.e. standard metabolic rate (R_s) and critical oxygen tension (P_crit) of red drum Sciaenops ocellatus were measured and scaled over a 2500‐fold range in mass (M_F; 0·26–686 g). R_s conformed to well established models (R_s = 3·73·91 M_F^?0·21; r² = 0·86) while P_crit increased over the size range (P_crit = 3·15 log₁₀M_F + 16·19; r² = 0·44). This relationship may be ecologically advantageous as it would allow smaller S. ocellatus to better utilize hypoxic zones as habitat and refuge from predators.     

THE SCALING OF PLANT AND ANIMAL BODY MASS,LENGTH, AND DIAMETER

The interspecific scaling exponents of body mass M and diameter D with respect to length L were determined to evaluate the predictions of three scaling hypotheses (geometric, stress, and elastic similitude). The relation between M and L was determined for data from a total of 133 aquatic and terrestrial species (66 plant and 67 animal species); the relation between D and L was determined independently for a total of 753 aquatic and terrestrial species (667 plant and 86 animal species). Organisms were crudely classified as to their geometry (spheres, spheroids, cylinders) and shape (defined as the body slenderness factor, L/D) to examine whether geometry and shape evinced size-dependent variations. Regression indicated M = 1.29L^2.95 (r² = 0.91, N = 133; α_RMA = 3.09 ± 0.088). The stress and elastic similitude (which respectively predict α_RMA = 5 and α_RMA = 4) were rejected; geometric similitude was not (α_RMA = 3). For animals and plants, α_RMA = 2.81 ± 0.061 (r² = 0.98), and α_RMA = 2.95 ± 0.093 (r² = 0.94), respectively. For aquatics and terrestrial organisms, α_RMA = 2.82 ±0.134 (r² = 0.97, N = 36), and α_RMA = 3.08 ±0.111 (r² = 0.89, N = 97), respectively. These results were interpreted to support the hypothesis of geometric similitude. For the pooled plant and animals data, D = 0.05L^1.00 (r² = 0.95; α_RMA = 1.03 ± 0.009), which was compatible with the hypothesis of geometric similitude. For plants, D = 0.05L^1.06 (r² = 0.95; α_RMA = 1.09). For animals, D = 0.29L^0.98 (r² = 0.95; α_RMA = 1.01 ± 0.025). Also, for aquatics, α_RMA = 0.951 ± 0.151, whereas for terrestrial plants and animals, α_RMA = 1.03 ± 0.089. Although the scaling exponent for D differed among individual groupings of animals and plants, the results of regression analyses were interpreted to indicate that, on the average, body diameter scaled isometrically with respect to length as predicted by geometric similitude. For the pooled data set, organic shape varied over 3 orders of magnitude; L varied over 9 orders of magnitude reflecting 22 orders of magnitude of M. In terms of body geometry and the absolute numbers of species in the total data set: spherical shaped species (L = D) < unassigned species < prolate spheroidal species < cylindrical (squat < slender) species. The largest organisms in the data set were slender (L/D > 20) cylindrical plants; the smallest organisms were spherical plants and animals. Although not subject to statistical inference, these data were interpreted to indicate that organic shape and geometry evince size-dependent variations. These variations as well as size-dependent changes in bulk density are hypothesized to account for the scaling exponents of M and D determined for individual plant and animal clades and grades.     

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.