Many calcified structures produce periodic growth increments useful for age determination at the annual or daily scale. However, age determination is invariably accompanied by various sources of error, some of which can have a serious effect on age-structured calculations. This review highlights the best available methods for insuring ageing accuracy and quantifying ageing precision, whether in support of large-scale production ageing or a small-scale research project. Included in this review is a critical overview of methods used to initiate and pursue an accurate and controlled ageing program, including (but not limited to) validation of an ageing method. The distinction between validation of absolute age and increment periodicity is emphasized, as is the importance of determining the age of first increment formation. Based on an analysis of 372 papers reporting age validation since 1983, considerable progress has been made in age validation efforts in recent years. Nevertheless, several of the age validation methods which have been used routinely are of dubious value, particularly marginal increment analysis. The two major measures of precision, average percent error and coefficient of variation, are shown to be functionally equivalent, and a conversion factor relating the two is presented. Through use of quality control monitoring, ageing errors are readily detected and quantified; reference collections are the key to both quality control and reduction of costs. Although some level of random ageing error is unavoidable, such error can often be corrected after the fact using statistical (‘digital sharpening)’ methods.

Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods

Pelagic marine predators face unprecedented challenges and uncertain futures. Overexploitation and climate variability impact the abundance and distribution of top predators in ocean ecosystems. Improved understanding of ecological patterns, evolutionary constraints and ecosystem function is critical for preventing extinctions, loss of biodiversity and disruption of ecosystem services. Recent advances in electronic tagging techniques have provided the capacity to observe the movements and long-distance migrations of animals in relation to ocean processes across a range of ecological scales. Tagging of Pacific Predators, a field programme of the Census of Marine Life, deployed 4,306 tags on 23 species in the North Pacific Ocean, resulting in a tracking data set of unprecedented scale and species diversity that covers 265,386 tracking days from 2000 to 2009. Here we report migration pathways, link ocean features to multispecies hotspots and illustrate niche partitioning within and among congener guilds. Our results indicate that the California Current large marine ecosystem and the North Pacific transition zone attract and retain a diverse assemblage of marine vertebrates. Within the California Current large marine ecosystem, several predator guilds seasonally undertake north-south migrations that may be driven by oceanic processes, species-specific thermal tolerances and shifts in prey distributions. We identify critical habitats across multinational boundaries and show that top predators exploit their environment in predictable ways, providing the foundation for spatial management of large marine ecosystems.

Tracking apex marine predator movements in a dynamic ocean

To quantify the occurrence of ingested plastic in fish species caught at different geographical positions in the North Sea, and to test whether the fish condition is affected by ingestion of plastics, 1203 individual fish of seven common North Sea species were investigated: herring, gray gurnard, whiting, horse mackerel, haddock, atlantic mackerel, and cod. Plastic particles were found in 2.6% of the examined fish and in five of the seven species. No plastics were found in gray gurnard and mackerel. In most cases, only one particle was found per fish, ranging in size from 0.04 to 4.8 mm. Only particles larger than 0.2 mm, being the diameter of the sieve used, were considered for the data analyses, resulting in a median particle size of 0.8 mm. The frequency of fish with plastic was significantly higher (5.4%) in the southern North Sea, than in the northern North Sea above 55°N (1.2%). The highest frequency (>33%) was found in cod from the English Channel. In addition, small fibers were initially detected in most of the samples, but their abundance sharply decreased when working under special clean air conditions. Therefore, these fibers were considered to be artifacts related to air born contamination and were excluded from the analyses. No relationship was found between the condition factor (size–weight relationship) of the fish and the presence of ingested plastic particles.

Plastic in North Sea Fish

1.Fishing spans all oceans and the impact on ocean predators such as sharks and rays is largely unknown. A lack of data and complicated jurisdictional issues present particular challenges for assessing and conserving high seas biodiversity. It is clear, however, that pelagic sharks and rays of the open ocean are subject to high and often unrestricted levels of mortality from bycatch and targeted fisheries for their meat and valuable fins.
2.These species exhibit a wide range of life-history characteristics, but many have relatively low productivity and consequently relatively high intrinsic vulnerability to over-exploitation. The IUCN — World Conservation Union Red List criteria were used to assess the global status of 21 oceanic pelagic shark and ray species.
3.Three-quarters (16) of these species are classified as Threatened or Near Threatened. Eleven species are globally threatened with higher risk of extinction: the giant devilray is Endangered, ten sharks are Vulnerable and a further five species are Near Threatened. Threat status depends on the interaction between the demographic resilience of the species and intensity of fisheries exploitation.
4.4. Most threatened species, like the shortfin mako shark, have low population increase rates and suffer high fishing mortality throughout their range. Species with a lower risk of extinction have either fast, resilient life histories (e.g. pelagic stingray) or are species with slow, less resilient life histories but subject to fisheries management (e.g. salmon shark).
5.5. Recommendations, including implementing and enforcing finning bans and catch limits, are made to guide effective conservation and management of these sharks and rays.


Copyright © 2008 John Wiley & Sons, Ltd.

http://baumlab.weebly.com/uploads/1/2/4/4/12445281/dulvy_2008.pdf

You can swim but you can't hide: the global status and conservation of oceanic pelagic sharks and rays

In this review we report new findings concerning interaction between marine debris and wildlife. Deleterious effects and consequences of entanglement, consumption and smothering are highlighted and discussed. The number of species known to have been affected by either entanglement or ingestion of plastic debris has doubled since 1997, from 267 to 557 species among all groups of wildlife. For marine turtles the number of affected species increased from 86 to 100 % (now 7 of 7 species), for marine mammals from 43 to 66 % (now 81 of 123 species) and for seabirds from 44 to 50 % of species (now 203 of 406 species). Strong increases in records were also listed for fish and invertebrates, groups that were previously not considered in detail. In future records of interactions between marine debris and wildlife we recommend to focus on standardized data on frequency of occurrence and quantities of debris ingested. In combination with dedicated impact studies in the wild or experiments, this will allow more detailed assessments of the deleterious effects of marine debris on individuals and populations.

/pdf/deleterious-effects-of-litter-on-marine-life-20031a25xa.pdf

Deleterious Effects of Litter on Marine Life

Elasmobranch reproductive behavior has been inferred from freshly caught specimens, laboratory examinations of reproductive structures and function, or determined from direct observations of captive or free swimming wild animals. Several general behaviors have been described including seasonal sexual segregation, courtship and copulation. Courtship behavior was inferred for many species from the presence of scars and tooth cuts on the female's body, and noted in more detail from underwater observations. Copulation has been directly observed in captive settings for several species of elasmobranchs in large aquaria, and in the wild for three species of urolophids and for Triaenodon obesus and Ginglymostoma cirratum. A detailed ‘case history’ of nurse shark reproductive behavior is presented that may be used as a template for future work on shark reproductive behavior of other species. Our studies, using diver identifiable tags and in situ behavioral observations, provide unprecedented information on social structure and mating behavior in this species. Since 1993, 115 G. cirratum, 45 adults and 70 juveniles have been tagged in the Dry Tortugas, Florida. Observations show that adult males visit the study site every year with three males dominant. Individual adult females visit the study area to mate in alternate years. Polygyny and polyandry are common. Future research on reproductive behavior of elasmobranchs should address questions on male access to females, sexual selection and dominance hierarchies.

A review of elasmobranch reproductive behavior with a case study on the nurse shark, Ginglymostoma cirratum

A large (4.6 m) white shark was followed for 3.5 days while its depth, water temperature and muscle temperature were recorded by acoustic telemetry. During this time the shark moved 190 km from an area south of Montauk Point, New York to Hudson Canyon. It made a number of brief excursions to the surface and to the bottom, but usually swam in the thermocline. Muscle temperature of the shark was as much as 5 C warmer than the water, confirming that a system of large retia mirabilia in the circulatory system function as heat exchangers. The shark did not thermoregulate and muscle temperature changed slowly as water temperature changed. The warming of the muscle as the shark swam into warmer water allowed us to estimate its rate of metabolism. The rate obtained is low and despite being warm, it appears that the shark can maintain itself for more than a month on a single large meal. The implications of this for its feeding habits are discussed.

https://www.jstor.org/stable/pdfplus/1444603.pdf

Temperature and Activities of a White Shark, Carcharodon carcharias

Spermatozoa stored in oviducal glands of sharks sampled off the North American east coast were revealed by viewing stained tissue sections using light microscopy. Of eleven species surveyed, sperm were found in nine:Alopias vulpinus, Lamna nasus, Carcharhinus obscurus, Carcharhinus plumbeus, Galeocerdo cuvieri, Prionace glauca, Rhizoprionodon terraenovae, Sphyrna lewini andSphyrna tiburo. Three insemination patterns are proposed to account for differences noted in these findings: (1) non-storage/immediate insemination for sharks such asLamna nasus; (2) short-term storage/delayed insemination as found in sharks in which ovulation is prolonged over weeks or months such asRhizoprionodon terraenovae, and (3) long-term storage/repeated insemination, a characteristic of nomadic sharks such asPrionace glauca andCarcharhinus obscurus which can store sperm in specialized tubules for months to years.

The storage of spermatozoa in the oviducal glands of western North Atlantic sharks

Age and growth of the sandbar shark (Carcharhinus plumbeus) was determined from rings in the vertebrae of 475 individuals, tagging data from 220 sharks at liberty for up to 17 yr, and length–freque...

Age and Growth of the Sandbar Shark (Carcharhinus plumbeus) from the Western North Atlantic

Age and growth rate of shortfin mako, Isurus oxyrinchus, captured by hook and line between 1961 and 1981 were determined using four methods: (1) temporal analysis of length–month information, (2) results of tagging data, (3) length–frequency analysis, and (4) ring counts on vertebrae. A temporal analysis of length–month information relating size to age for individuals less than 150 cm fork length (FL) was used to determine size (60–70 cm FL), time of birth (late spring), and early growth rate (50 cm/yr for ages 0–I, 32 cm/yr for ages I–II). This growth rate was used as a basis for interpreting the accuracy of other methods. Annual growth rates were calculated from 32 tag–recaptured mako sharks and resolved graphically into a growth curve. Length–frequency modes extended age estimates to intermediate-sized makos. Counts of growth rings on vertebral centra stained with silver nitrate were employed to back-calculate lengths at ages for the full range (69–328 cm). Our interpretation was based on the hypothesi...

Harold L. Pratt

Papers

A review of elasmobranch reproductive behavior with a case study on the nurse shark, Ginglymostoma cirratum

Temperature and Activities of a White Shark, Carcharodon carcharias

The storage of spermatozoa in the oviducal glands of western North Atlantic sharks

Age and Growth of the Sandbar Shark (Carcharhinus plumbeus) from the Western North Atlantic

Age and growth of the shortfin Mako, Isurus oxyrinchus, using four methods