Allen H. Andrews

Age determination and validation studies of marine fishes: do deep-dwellers live longer?

Age determination and validation studies on deep-water marine fishes indicate they are difficult to age and often long-lived. Techniques for the determination of age in individual fish includes growth-zone analysis of vertebral centra, fin rays and spines, other skeletal structures, and otoliths (there are three sets of otoliths in most bony fish semicircular canals, each of which is made of calcium carbonate). Most have regular increments deposited as the fish (and its semicircular canals) grows. The most commonly used otolith for age determination is the largest one called the sagitta. Age validation techniques include: (1) tag-recapture, often combined with oxytetracycline injection and analysis in growth-zones of bone upon recapture; (2) analysis of growth-zones over time; and (3) radiometric approaches utilizing a known radioactive decay series as an independent chronometer in otoliths from bony fishes. We briefly summarize previous studies using these three validation approaches and present results from several of our radiometric studies on deep-water, bony fishes recently subjected to expanding fisheries. Radiometric age validation results are presented for four species of scorpaenid fishes (the bank, Sebastes rufus, and bocaccio, S. paucispinis, rockfishes, and two thornyhead species, Sebastolobus altivelis and S. alascanus). In addition, our analysis of scorpaenids indicates that longevity increases exponentially with maximum depth of occurrence. The reason that the deep-water forms of scorpaenid fishes are long-lived is uncertain. Their longevity, however, may be related to altered physiological processes relative to environmental parameters like low temperature, high pressures, low light levels, low oxygen, and poor food resources.

Age, growth and radiometric age validation of a deep-sea, habitat-forming gorgonian (Primnoa resedaeformis) from the Gulf of Alaska

Sustainable fisheries require (1) viable stock populations with appropriate harvest limits and (2) appropriate habitat for fish to survive, forage, seek refuge, grow and reproduce. Some deep-water habitats, such as those formed by deep-water stands of coral, may be vulnerable to fishing disturbance. The rate at which habitat can be restored is a critical aspect of fishery management. The purpose of this study was to characterize growth rates for a habitat-forming deep-sea coral. Two nearly complete colonies of red tree coral (Primnoa resedaeformis) collected from waters off southeast Alaska were used for an analysis of age and growth characteristics. CAT scans revealed that colonies consisted of multiple settlement events, where older basal structures provided for settlement of new colonies. The decay of 210Pb over the length of the colony was used to validate age estimates from growth ring counts. Age estimates were over 100 yr for sections near the heavily calcified base. Based on validated growth ring counts, growth of red tree coral ranged from 1.60 to 2.32 cm per year in height and was approximately 0.36 mm per year in diameter. These growth rates suggest that the fishery habitat created by red tree coral is extremely vulnerable to bottom fishing activities and may take over 100 years to recover.

Investigations of Δ14C, δ13C, and δ15N in vertebrae of white shark (Carcharodon carcharias) from the eastern North Pacific Ocean

The white shark, Carcharodon carcharias, has a complex life history that is characterized by large scale movements and a highly variable diet. Estimates of age and growth for the white shark from the eastern North Pacific Ocean indicate they have a slow growth rate and a relatively high longevity. Age, growth, and longevity estimates useful for stock assessment and fishery models, however, require some form of validation. By counting vertebral growth band pairs, ages can be estimated, but because not all sharks deposit annual growth bands and many are not easily discernable, it is necessary to validate growth band periodicity with an independent method. Radiocarbon (14C) age validation uses the discrete 14C signal produced from thermonuclear testing in the 1950s and 1960s that is retained in skeletal structures as a time-specific marker. Growth band pairs in vertebrae, estimated as annual and spanning the 1930s to 1990s, were analyzed for Δ14C and stable carbon and nitrogen isotopes (δ13C and δ15N). The aim of this study was to evaluate the utility of 14C age validation for a wide-ranging species with a complex life history and to use stable isotope measurements in vertebrae as a means of resolving complexity introduced into the 14C chronology by ontogenetic shifts in diet and habitat. Stable isotopes provided useful trophic position information; however, validation of age estimates was confounded by what may have been some combination of the dietary source of carbon to the vertebrae, large-scale movement patterns, and steep 14C gradients with depth in the eastern North Pacific Ocean.

Lead-radium dating of orange roughy (Hoplostethus atlanticus): validation of a centenarian life span

Life-span estimates for orange roughy (Hoplostethus atlanticus) range from ~20 years to well over 100 years. In this study, an improved lead-radium dating technique provided independent age estimates from sagittal otoliths. This tech- nique used the known properties of radioactivity for lead-210 and radium-226 to determine the validity of fish age esti- mates. An improvement to lead-radium dating using mass spectrometry allowed the use of smaller samples than previously possible; therefore, an application was made to otolith cores, the first few years of otolith growth. This ap- proach circumvented the use of whole otoliths and alleviated many of the assumptions that were necessary in previous lead-radium dating applications. Hence, it was possible to critically evaluate lead-radium dating as a tool in fish age vali- dation. The measurement of lead-radium ratios for a series of age groups that consisted of otolith cores, grouped based on growth-zone counts from thin sections, showed a high degree of correlation to the expected lead-radium ingrowth curve. This finding provided support for age estimation procedures using thin otolith sectioning. As independent estimates of age, the results indicated that fish in the oldest age group were at least 93 years old, providing robust support for a centenarian life span.

Radiometric age validation of the yelloweye rockfish (Sebastes ruberrimus) from southeastern Alaska

etsilaunk, . M.l Abstract. The yelloweye rockfish (Sebastes ruberrimus), a dominant component of an important deep-water rockfish fishery of the Gulf of Alaska, is thought to be long-lived with an estimated longevity exceeding 100 years. For the purpose of monitoring stocks, age is routinely estimated by counting growth zones in otolith cross-sections using the break-and-burn technique; however, such age estimates for this species have remained unvalidated. To evaluate these age data, age estimations from the break-and-burn technique were corroborated by comparing results from transverse sectioning of otoliths. The agreement between the techniques was excellent and each technique had a very low coefficient of variation (3.6% and 4.5%). Radiometric age validation of these estimates was performed on the otolith core material (first three years of growth) of pooled age groups having an average estimated age of 27.4-101.4 years. Agreement was variable and somewhat subjective, but radiometric data support ages estimated from otolith growth zone counts. The strongest support for age that exceeds 100 years comes from the observation that as age derived from growth zones approached and exceeded 100 years, the sample ratios measured ( 210 Pb: 226 Ra) approached equilibrium. The radiometric results of our study validate the estimates derived from growth zones and the age estimating procedures, which confirms that the longevity of yelloweye rockfish exceeds 100 years.

Bomb radiocarbon dating of three important reef-fish species using Indo-Pacific D14C chronologies

Demersal reef fishes of the Indo-Pacific are under increasing pressure as a fisheries resource, yet many of the important life history characteristics required for suitable management are poorly known. The three fish species, eightbar grouper (Hyporthodus octofasciatus), ruby snapper (Etelis carbunculus) and the spangled emperor (Lethrinus nebulosus), are important components of fisheries and ecosystems throughout the Indo-Pacific. Despite their importance, age and growth information is incomplete. Age has been estimated for E. carbunculus and L. nebulosus, but validated age beyond the first few years is lacking and for H. octofasciatus no age estimates exist. Bomb radiocarbon dating can provide age estimates that are independent of growth-zone counting, but only if appropriate reference Δ14C chronologies exist. In this study, a series of Δ14C records from hermatypic corals was assembled to provide a basis for bomb radiocarbon dating in the western Indo-Pacific region. Results provided (1) valid age estimates for comparison to age estimates from two facilities investigating growth-zones in otolith thin sections; (2) support for age estimation protocols using otolith thin sections; and (3) the information necessary for further refinement of age estimation procedures. Estimates of longevity from bomb radiocarbon dating agree with some prior studies: H. octofasciatus, E. carbunculus and L. nebulosus all being long-lived species with life spans of at least 43, 35 and 28 years respectively.

Fish faunal and habitat analyses using trawls, camera sleds and submersibles in benthic deep-sea habitats off central California

Abstract Beam trawl, camera sled and submersible data from 2 000–3 300 m off central California produced similar fish faunal composition, but different density estimates. All species caught in trawls were observed in camera-sled and submersible observations. However, some rare species that were observed were not caught in trawls. The fish fauna was dominated by the families Macrouridae, Zoarcidae, Moridae, and Rajidae. Fishes both trawled and observed were the macrourids Coryphaenoides armatus, C. filifer and C. leptolepis; the zoarcids Bothrocara spp., Pachycara lepinium and Lycenchelys spp.; the morid Antimora microlepis; the rajid Bathyraja trachura, the ophidiid Spectrunculus grandis, and the liparidid Careproctus ovigerum. One unidentified liparidid (Paraliparis sp.) and two unidentified Lycenchelys spp. were trawled and may have been seen but also could not be identified to species from photographs. Observed only in photographs were the liparidids Paraliparis rosaceus and Careproctus melanurus, synodontid Bathysaurus mollis, and notocanthid Notacanthus chemnitzii. These three techniques differed in their ability to provide specimens for accurate identification, counts, and later life history (feeding habit, age and growth, and reproduction) studies, and to provide information on dispersion, habitat utilization, behavior and interactions. Accurate density estimates were undoubtedly hampered by trawl and camera sled avoidance, escape, and uncertainties concerning the area trawled. Camera sleds produced higher (and perhaps better) estimates of density. Submersible observations from the DSV Alvin produced a similar species list but little additional, quantitative information. Both visual techniques allowed habitat characterization, but no strong faunal associations with habitat types were observed.

Bomb radiocarbon and lead-radium disequilibria in otoliths of bocaccio rockfish (Sebastes paucispinis): a determination of age and longevity for a difficult-to-age fish

Longevity estimates for the bocaccio rockfish (Sebastes paucispinis) using traditional techniques range from less than 20 years to approximately 50 years. Otoliths of bocaccio are difficult to age, and previous attempts to validate ages have been unsuccessful. Because otolith age suggests the bocaccio are reasonably long-lived, lead-radium dating was used in an attempt to independently age bocaccio otoliths. The measured 210 Pb and 226 Ra activities were among the lowest reported and resulted in poor radiometric age resolution; however, the break- and-burn technique clearly underestimated age in some cases with the longevity of the bocaccio being at least 31 years. To provide better age resolution, the bomb radiocarbon approach was applied to individual otoliths. Based on measured radiocarbon levels relative to a reference time-series, several specimens were aged at approximately 30-40 years. To evaluate these determinations, the remaining otolith of the pair was sectioned and aged blind. The result was an excellent fit to the reference time-series and a validation of the age estimates. The maximum age from growth zone counts was 37 ± 2 years, which is consistent with a reported maximum age of approximately 50 years.

Investigations of age and growth for three deep-sea corals from the Davidson Seamount off central California

A recent biological characterization of the Davidson Seamount off central California using a remotely operated vehicle revealed communities rich with deep-sea corals. During this characterization several corals were collected and three colonies were made available for an age and growth study. The colonies examined were identified as bubblegum coral (Paragorgia sp.), bamboo coral (Keratoisis sp.), and precious coral (Corallium sp.). Age was estimated from growth zone counts made in skeletal cross sections. These age estimates were used to estimate growth rates and colony age. Estimated growth rates determined for each species were quite different. The bubblegum coral had a relatively high estimated growth rate, with the precious and bamboo coral estimated as slow growing. These age and growth observations were evaluated relative to published studies on related species and an attempt was made to validate the age and growth estimates with an independent radiometric ageing technique (i.e., lead-210 dating). This approach was not successful for the bubblegum coral, and was successful for the bamboo and precious corals to differing degrees. For the bamboo coral, a minimum colony age of over 200 years was determined. For the precious coral, a linear growth rate of approximately 0.25 cm/yr led to a colony age of about 115 years; however, based on the radial growth rate, an age of up to 200 year is possible.

Axial rod growth and age estimation of the sea pen, Halipteris willemoesi Kölliker

Halipteris willemoesi is a large octocoral commonly found in the Bering Sea. It is a member of a ubiquitous group of benthic cnidarians called sea pens (Octocorallia: Pennatulacea). Sea pens have a skeletal structure, the axial rod, that in cross section exhibits growth rings. Pairs of adjacent rings, or ring couplets, were assumed to be annuli and were used to estimate the age and growth of H. willemoesi. Twelve axial rods, extracted from H. willemoesi collected in the Bering Sea, were selected to represent small (25–29 cm total length), medium (97–130 cm TL) and large (152–167 cm TL) colonies. Each rod resembled a tapered dowel; the thickest part (0.90–6.75 mm in diameter) was at about 5–10% of total length from the base tip, the distal part was more gradually tapered than was the base. The number of ring couplets increased with rod size indicating their utility in estimating age and growth. Estimated age among rods was based on couplet counts at the thickest part of each rod; the average estimated age (±SE) was 7.1 ±0.7, 19.3 ±0.5, and 44.3 ±2.0 yr for small, medium and large-size rods, respectively. Based on these estimated ages, average growth rate in total length was 3.9 ± 0.2, 6.1 ± 0.3, and 3.6 ± 0.1 cm yr−1 for small, medium, and large-size colonies. The average annual increase in maximum rod diameter among all colonies was 0.145 ± 0.003 SE mm yr−1; therefore, age prediction from maximum rod diameter was calculated (estimated age (yr) = 7.0 * (maximum rod diameter, mm) −0.2; R2 = 0.99). At maximum diameter, the average couplet width was relatively constant among the three colony sizes (0.072 ± 0.05 mm). X-ray diffraction and electron microprobe analyses revealed that the inorganic portion of the rod is composed of a high-magnesium calcite. Radiometric validation of these age and growth rate estimates was attempted, but high amounts of exogenous 210Pb precluded using the disequilibria of 210Pb:226Ra. Instead, 210Pb activities were measured in a series of cores extracted along the axial rod. These activities ranged from 0.691 ± 0.036 (SE) to 2.76 ± 0.13 dpm g−1, but there was no pattern of decay along the length of the rod; therefore, the growth rates and corresponding ages could not be validated. Based on estimated age from ring couplet counts, growth in total rod length is slow at first, fastest at medium size, and slows toward maximum size, with an estimated longevity approaching 50 yr.