Fish assemblages associated with three types of artificial reefs: density of assemblages and possible impacts on adjacent fish abundance

We evaluated the effectiveness of wooden artificial reefs (ARs) as fish habitat. Three types of ARs, made of cedar logs, broadleaf tree logs, and PVC pipes, respectively, were deployed in triplicate at 8-m depth off Maizuru, Kyoto Prefecture, Sea of Japan, in May 2004. Fish assemblages associated with each of the nine ARs were observed by using SCUBA twice a month for four years. Fish assemblages in the adjacent habitat were also monitored for two years before and four years after reef deployment. In the surveyed areas (ca. 10 m2) associated with each of the cedar, broadleaf, and PVC ARs, the average number of fish species was 4.14, 3.49, and 3.00, and the average number of individuals was 40.7, 27.9, and 20.3, respectively. The estimated biomass was also more greater when associated with the cedar ARs than with other ARs. Visual censuses of the habitat adjacent to the ARs revealed that the number of fish species and the density of individuals were not affected by the deployment of the ARs. Our results support the superiority of cedar as an AR material and indicate that deployment of wooden ARs causes no reduction of fish abundance in adjacent natural reefs.

Effects of starvation on energy density of juvenile chum salmon (Oncorhynchus keta) captured in marine waters of Southeastern Alaska

We conducted laboratory starvation experiments on juvenile chum salmon (Oncorhynchus keta) captured in the neritic marine waters of northern Southeast Alaska in June and July 2003. Temporal changes in fish energy density (whole body energy content [WBEC], cal/g dry weight), percent moisture content, wet weight (g), length (mm), and size-related condition residuals were measured in the laboratory and were then compared to long-term field data. Laboratory water temperatures and salinities averaged 9°C and 32 psu in both months. Trends in response variables were similar for both experimental groups, although sampling intervals were limited in July because fewer fish were available (n= 54) than in June (n=101). Overall, for June (45-d experimental period, 9 intervals), WBEC, wet weight, and condition residuals decreased and percent moisture content increased, whereas fork length did not change. For July (20-d experimental period, 5 intervals), WBEC and condition residuals decreased, percent moisture content and fork length increased, and wet weight did not change. WBEC, percent moisture content, and condition residuals fell outside the norm of longterm data ranges within 10–15 days of starvation, and may be more useful than fork length and wet weight for detecting fish condition responses to suboptimal environments.

Reproductive biology of blue marlin (Makaira nigricans) in the western Pacific Ocean

The reproductive biology of blue marlin (Makaira nigricans) was assessed from 1001 fish (ranging from 121 to 275 cm in eye-to-fork length; EFL) caught by Taiwanese offshore longliners in the western Pacific Ocean from September 2000 to December 2001 and from 843 gonad samples from these fish, The overall sex ratio of the catch was approximately 1:1 dur ing the sampling period, but blue marlin are sexually dimorphic; females are larger than males. Reproductive activity (assessed by histology), a gonadosomatic index, and the distribution of oocyte diameters, indicated that spawning occurred predominantly from May to September. The estimated sizes-at-maturity (EFL50) were 179.76 ±1.01 cm (mean ±standard error) for females and 130 ±1 cm EFL for males. Blue marlin are multiple spawners and oocytes develop asynchronously. The proportion of mature females with ovaries containing postovulatory follicles (0.41) and hydrated oocytes (0.34) indicated that the blue marlin spawned once every 2–3 days on average. Batch fecundity (BF) for 26 females with the most advanced oocytes (≥1000 μm), but without postovulatory follicles, ranged from 2.11 to 13.50 million eggs (6.94 ± 0.54 million eggs). The relationships between batch fecundity (BF, in millions of eggs) and EFL and round weight (RW, kg) were BF = 3.29 × 10 –12 EFL5.31 (r2 = 0.70) and BF = 1.59 × 10–3 RW 1.73 (r2= 0.67), respectively. The parameters estimated in this study are key information for stock assessments of blue marlin in the western Pacific Ocean and will contribute to the conservation and sustainable yield of

Electrical phase angle as a new method to measure fish condition

In this study, phase angle (the ratio of resistance and reactance of tissue to applied electrical current) is presented as a possible new method to measure fish condition. Condition indices for fish have historically been based on simple weight-at-length relationships, or on costly and timeconsuming laboratory procedures that measure specific physiological parameters. Phase angle is introduced to combine the simplicity of a quick field-based measurement with the specificity of laboratory analysis by directly measuring extra- and intracellular water distribution within an organism, which is indicative of its condition. Phase angle, which can be measured in the field or laboratory in the time it takes to measure length and weight, was measured in six species of fish at different states (e.g., fed vs. fasted, and postmortem) and under different environmental treatments (wild vs. hatchery, winter vs. spring). Phase angle reflected different states of condition. Phase angles <15° indicated fish in poor condition, and phase angles >15° indicated fish that were in better condition. Phase angle was slightly affected by temperatures (slope = – 0.19) in the 0–8°C range and did not change in fish placed on ice for <12 hours. Phase angle also decreased over time in postmortem fish because of cell membrane degradation and subsequent water movement from intra- to extracellular (interstitial) spaces. Phase angle also reflected condition of specific anatomical locations within the fish.

Surface mucous as a source of genomic DNA from Atlantic billfishes (Istiophoridae) and swordfish (Xiphiidae)

Procedures for sampling genomic DNA from live billfishes involve manual restraint and tissue excision that can be difficult to carry out and may produce stresses that affect fish survival. We examined the collection of surface mucous as a less invasive alternative method for sourcing genomic DNA by comparing it to autologous muscle tissue samples from Atlantic blue marlin (Makaira nigricans), white marlin (Tetrapturus albidus), sailfish (Istiophorus platypterus), and swordfish (Xiphias gladius). Purified DNA from mucous was comparable to muscle and was suitable for conventional polymerase chain reaction, random amplified polymorphic DNA analysis, and mitochondrial and nuclear locus sequencing. The nondestructive and less invasive characteristics of surface mucous collection may promote increased survival of released specimens and may be advantageous for other marine fish genetic studies, particularly those involving large live specimens destined for release.

Anadromous fish as marine nutrient vectors

The tidal freshwater of Virginia supports anadromous herring (Alosa spp.) spawning runs in the spring; however, their importance as nutrient delivery vectors to the freshwater fish food web remains unknown. The stable isotope signatures of fishes from 21 species and four different guilds (predators, carnivores, generalists, and planktivores) were examined in this study to test the hypothesis that marine derived nutrients (MDNs) brought by anadromous fish would be traced into the guilds that incorporated them. Spawning anadromous fish were 13C and 34S-enriched (δ13C and δ34S of approximately 18‰ and 17.7‰, respectively) relative to resident freshwater fish. Of the guilds examined, only predators showed 13C and 34S-enrichment similar to the anadromous fish; however, some generalist catfish also showed enriched signatures. Specific fatty acid δ13C signatures for gizzard shad (Dorosoma cepedianum), blue catfish (Ictalurus furcatus), and alewife (Alosa pseudoharengus), show a 10‰ range among fishes, clearly reflecting isotopically distinct dietary sources. The δ13C and δ34S distribution and range among the freshwater fishes suggest that both autochthonous and allochthonous (terrestrial C3 photosynthetic production and MDN) nutrient sources are important to the tidal freshwater fish community.

Assessment of fish populations and habitat on Oculina Bank, a deep-sea coral marine protected area off eastern Florida

A portion of the Oculina Bank located off eastern Florida is a marine protected area (MPA) preserved for its dense populations of the ivory tree coral (Oculina varicosa), which provides important habitat for fish. Surveys of fish assemblages and benthic habitat were conducted inside and outside the MPA in 2003 and 2005 by using remotely operated vehicle video transects and digital still imagery. Fish species composition, biodiversity, and grouper densities were used to determine whether O. varicosa forms an essential habitat compared to other structure-forming habitats and to examine the effectiveness of the MPA. Multivariate analyses indicated no differences in fish assemblages or biodiversity among hardbottom habitat types and grouper densities were highest among the most complex habitats; however the higher densities were not exclusive to coral habitat. Therefore, we conclude that O. varicosa was functionally equivalent to other hardbottom habitats. Even though fish assemblages were not different among management areas, biodiversity and grouper densities were higher inside the MPA compared to outside. The percentage of intact coral was also higher inside the MPA. These results provide initial evidence demonstrating effectiveness of the MPA for restoring reef fish and their habitat. This is the first study to compare reef fish populations on O. varicosa with other structure-forming reef habitats and also the first to examine the effectiveness of the MPA for restoring fish populations and live reef cover.

A comparison between warm-water fish assemblages of Narragansett Bay and those of Long Island Sound waters

Fish species of warmwater origin appear in northeastern U.S. coastal waters in the late summer and remain until late fall when the temperate waters cool. The annual abundance and species composition of warm-water species is highly variable from year to year, and these variables may have effects on the trophic dynamics of this region. To understand this variability, records of warm-water fish occurrence were examined in two neighboring temperate areas, Narragansett Bay and Long Island Sound. The most abundant fish species were the same in both areas, and regional abundances peaked in both areas in the middle of September, four weeks after the maximum temperature in the middle of August. On average, abundance of warm-water species increased throughout the years sampled, although this increase can not be said to be exclusively related to temperature. Weekly mean temperatures between the two locations were highly correlated (r= 0.99; P<0.001). The warm-water fish faunas were distinctly different in annual abundances in the two areas for each species by year (1987–2000), and these differences ref lect the variability in the transport processes to temperate estuaries. The results reveal information on the abundance of warm-water fish in relation to trends toward warmer waters in these region

Fishes associated with pelagic Sargassum and open water lacking Sargassum in the Gulf Stream off North Carolina

The community structure of fishes associated with pelagic Sargassum spp. and open water lacking Sargassum was examined during summer and fall cruises, 1999–2003, in the Gulf Stream off North Carolina. Significantly more individual fishes (n= 18,799), representing at least 80 species, were collected from samples containing Sargassum habitat, compared to 60 species (n=2706 individuals) collected from openwater habitat. The majority (96%) of fishes collected in both habitats were juveniles, and planehead filefish (Stephanolepis hispidus) dominated both habitats. Regardless of sampling time (day or night), Sargassum habitat yielded significantly higher numbers of individuals and species compared with open-water collections. Overall, fishes collected by neuston net tows from Sargassum habitat were significantly larger in length than fishes collected from open-water habitat with neuston nets. A significant positive, linear relationship existed between numbers of fishes and the quantity of Sargassum collected by neuston net. Underwater video recordings indicated a layered structure of fishes among and below the algae and that smaller fishes were more closely associated with the algae than larger fishes. Observations of schooling behaviors of filefishes (Monacanthidae), dolphinfish (Coryphaena hippurus), and jacks (Carangidae), and fish-jellyfish associations were also recorded with an underwater video camera. Our data indicate that Sargassum provides a substantial nursery habitat for many juvenile fishes off the U.S. southeast coast.

Habitat and bycatch effects on population parameters of inshore lizardfish (Synodus foetens) in the north central Gulf of Mexico

We examined the effect of habitat and shrimp trawl bycatch on the density, size, growth, and mortality of inshore lizardfish (Synodus foetens), a nonexploited species that is among the most widespread and abundant benthic fishes in the north central Gulf of Mexico. Results of quarterly trawl sampling conducted from spring 2004 through spring 2005 revealed that inshore lizardfish are most abundant on sand habitat, but larger fish are more common on shell rubble habitat. There was no significant difference in fish density between habitats exposed to shrimp trawling on the open shelf versus those habitats within a permitted artificial reef zone that served as a de facto no-trawl area; this finding indicates that either inshore lizardfish experienced minimal effects from trawling or, more likely, that fish moved between trawled and nontrawled habitats. Exploitation ratio (bycatch mortality/total morality) estimates derived from catch curve analysis ranged from 0.43 inside the artificial reef zone to 0.55 outside the reef zone, thus indicating that inshore lizardfish are subject to significant fishing mortality in the north central Gulf of Mexico despite the lack of a directed fishery for the species. We infer from this result that effects of shrimp trawl bycatch may be significant at the population level for nonexploited species and that a broader ecosystem-scale examination of bycatch effects is warranted.

Catches in ghost-fishing octopus and fish traps in the northeastern Atlantic Ocean (Algarve, Portugal)

Ghost fishing is the term used to describe the continued capture of fish and other living organisms after a fisherman has lost all control over the gear. Traps may be lost for a variety of reasons including theft, vandalism, abandonment, interactions with other gear, fouling on the bottom (i.e., traps and ropes are caught on rocky substrate), bad weather, and human error (Laist, 1995). Annual trap loss can be as high as 20% to 50% of fished traps in some fisheries (Al-Masroori et al., 2004). Because lost traps can continue to fish for long periods, albeit with decreasing efficiency over time (e.g., Smolowitz, 1978; Breen, 1987, 1990; Guillory, 1993), ghost fishing is a concern in fisheries worldwide.

Advantages of using crest nets to sample presettlement larvae of reef fishes in the Caribbean Sea

Identifying the spatial and temporal patterns of larval fish supply and settlement is a key step in understanding the connectivity of meta-populations (Sale et al., 2005). Because of the potentially dispersive nature of the pelagic larval phase of most reef fishes, tracking cohorts from hatching to settlement is extremely difficult (but see Jones et al., 1999). However, for many studies it is sufficient to sample larvae immediately before settlement. Many coral reef fish species use mangrove and seagrass beds as nursery habitats (Nagelkerken et al., 2001; Mumby et al., 2004) and larvae of these species must pass over the reef crest in order to arrive at their preferred settlement habitats. The ability to sample this new cohort of larval fishes provides opportunities for researchers to explore the intricacies of the transition from larva to juvenile (Searcy and Sponaugle, 2001). Quantifying the potential settlers also provides valuable information about the spatial and temporal supply of presettlement larvae (Victor, 1986). Therefore a number of larval sampling methods were developed, one of which is the use of crest nets (Dufour and Galzin, 1993).

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.

Changes in egg production of the western rock lobster (Panulirus cygnus) associated with appendage damage

Data collected during fish-ery-independent sampling programs were used to examine the impact of appendage damage (indicated by lost or regenerated legs and antennae) on the reproductive output of female western rock lobster (Panulirus cygnus). Most of the damaged females sampled had one (53%), two (27%), or three (13%) appendages that had been lost or that were regenerating. Appendage damage was associated with the reduced probability of a female developing ovigerous setae; and if setae were produced, with the reduced probability that females would produce more than one batch of eggs within a season. These effects were more pronounced as the number of damaged appendages increased. From data collected in 2002, it was estimated that the total number of eggs produced by mature females caught in the fishery was significantly reduced (P<0.001) by 3–9% when the impact of appendage damage was included.

Implications of substrate complexity and kelp variability for south-central Alaskan nearshore fish communities

Understanding the interactions between kelp beds and nearshore fish is essential because anthropogenic changes and natural variability in these beds may affect available habitat for fishes. In this study fish communities were investigated in south-central Alaska kelp beds characterized by a range of substrate complexity and varying densities of both perennial understory kelps and annual canopy kelps. Many of the observed fish species, as well as understory and canopy kelps, were positively associated with structurally complex substratum. Targeted canopy and understory kelp beds supported seasonal populations of adult and juvenile Pacific cod (Gadus macrocephalus), rockfishes (Sebastes spp.), and year-round populations of greenlings (Hexagrammos spp.). Monthly changes in kelp and fish communities ref lected seasonal changes; the densities of some species were greatest during periods with higher temperatures. This work illustrates the importance of structurally complex kelp beds with persistent understory kelp populations as important fish habitat for several commercially and recreationally important fishes.