Cross Seamount Research Articles

Geographic distribution of the Cross Seamount beaked whale based on acoustic detections

AbstractBeaked whales produce frequency‐modulated echolocation pulses that appear to be species‐specific, allowing passive acoustic monitoring to play a role in understanding spatio‐temporal patterns. The Cross Seamount beaked whale is known only from its unique echolocation signal (BWC) with no confirmed species identification. This beaked whale spans the Pacific Ocean from the Mariana Archipelago to Baja California, Mexico, south to the equator, but only as far north as latitude 29°N. Within these warm waters, 92% of BWC detections occurred at night, 6% during crepuscular periods, and only 2% during daylight hours. Detections of BWC signals on drifting recorders with a vertical hydrophone array at 150 m depth demonstrated that foraging often occurred shallow in the water column (<150 m). No other species of beaked whale to date has been documented foraging in waters this shallow. Given their nocturnal, shallow foraging dives, this species appears to prefer prey that may be available in the water column only during those hours. The foraging behavior of Cross Seamount beaked whales appears to be unique among all beaked whales, and these findings contribute additional ecological and acoustic information which can help guide future efforts to identify this cryptic whale.

Dive characteristics of Cross Seamount beaked whales from long‐term passive acoustic monitoring at the Pacific Missile Range Facility, Kauaʻi

AbstractBeaked whale foraging pulses were detected on the Pacific Missile Range Facility (PMRF) off Kauaʻi, Hawaiʻi, via long term passive acoustic monitoring. The unidentified pulses do not match foraging pulses of known species on the range but are similar to the unidentified beaked whale first detected at Cross Seamount, Hawaiʻi. Although there has not been a visual confirmation of the unidentified beaked whale species, analysis of data collected from 2007 to 2019 has identified beaked whale foraging dive characteristics from echolocation pulses. From the 13 years of data, the most distinct patterns were that all foraging dives occurred at night and the nighttime foraging dive rate was 0.11 group vocal periods (GVP) per hour, with most detections on shallow hydrophones (625–1,000 m deep) over steep bathymetric slopes. Data collected during U.S. Navy training events were used to compare dive behavior during mid‐frequency active sonar (MFAS) activity against baseline periods; it was determined that the whales reduced GVPs during sonar and these remained low for at least 3 days after the training events. These results are the first long‐term record of acoustic signals from the Cross Seamount beaked whale and provide important insights into their habitat use and occurrence patterns.

Seamount effects on micronekton at a subtropical central Pacific seamount

Seamounts are globally ubiquitous features with potential for increased biodiversity and biomass, including those of economically important fish. Although their ecological and economical importance is well known, the mechanisms for supporting seamount-associated communities are not well understood. In this study, the effects of an intermediate depth seamount (Cross Seamount) on the micronekton communities, forage for economically important bigeye tuna, are investigated. Relative biomass and composition estimates were calculated from multi-frequency active acoustic data from surveys over 3 years. Mean micronekton biomass was significantly higher than in the ambient environment and its composition differed over the flanks and plateau of Cross Seamount. The effects of the seamount extended ∼3.5 km away from the plateau's edge, possibly further below 400 m depth at the flanks. Micronekton occupied the water column from the surface to the 400 m deep plateau with dense aggregations immediately over the bottom at night. During the day, these micronekton migrated both horizontally and downward, occupying depths of 500–700 m, preferably along the upstream flank of the seamount. Descending micronekton from near-surface waters appeared to be temporarily blocked by the topography before swimming below the plateau at the flanks. Mechanisms supporting the increase in micronekton biomass are uncertain, although hydrographic data support topographic trapping of zooplankton and the existence of transient or semi-permanent Taylor caps.

Long-term foraging dive characteristics of Cross Seamount beaked whales at the Pacific Missile Range Facility

Beaked whale foraging dive clicks similar to those detected at Cross Seamount were detected during passive acoustic monitoring of marine mammals at the Pacific Missile Range Facility (PMRF) off Kauai, Hawaii using bottom-mounted hydrophones from January 2007 through August 2018. The Cross Seamount beaked whale (BWC) foraging dive click frequency sweeps from approximately 18 kHz to above the recording bandwidth of the PMRF sensors of 48 kHz at inter-click-intervals of 0.14 s (std 0.06 s). These unique clicks have only been detected at Cross Seamount and around the Hawaiian Islands, and because they have only been detected at night there has been no visual detections or species confirmation. However, they are distinctive enough to automatically detect, and can be used to describe basic presence at PMRF. Detections averaged 0.047 dives/h (in a 24-h cycle), and occurred almost entirely on the southern part of the range (water depth <1000 m). 702 BWC foraging dives were used to determine a foraging dive baseline over a 12-year period, to compare foraging dive rates during US Naval exercise events and baseline periods, and to contrast BWC foraging dive behavior from Blainville’s beaked whale foraging dive behavior at PMRF.Beaked whale foraging dive clicks similar to those detected at Cross Seamount were detected during passive acoustic monitoring of marine mammals at the Pacific Missile Range Facility (PMRF) off Kauai, Hawaii using bottom-mounted hydrophones from January 2007 through August 2018. The Cross Seamount beaked whale (BWC) foraging dive click frequency sweeps from approximately 18 kHz to above the recording bandwidth of the PMRF sensors of 48 kHz at inter-click-intervals of 0.14 s (std 0.06 s). These unique clicks have only been detected at Cross Seamount and around the Hawaiian Islands, and because they have only been detected at night there has been no visual detections or species confirmation. However, they are distinctive enough to automatically detect, and can be used to describe basic presence at PMRF. Detections averaged 0.047 dives/h (in a 24-h cycle), and occurred almost entirely on the southern part of the range (water depth <1000 m). 702 BWC foraging dives were used to determine a foraging dive baseli...

Seismoacoustic observations at deep ocean observatories: ACO, H2O, and OSN1

Deep seafloor (~5000 m) observations of seismoacoustic arrivals are presented from the Aloha Cabled Observatory (ACO), Hawaii-2 Observatory (H20), and Ocean Seismic Network-1 (OSN1). Acoustic observations of local earthquakes from the ACO 24 kHz hydrophone show extraordinarily high frequencies up to 165 Hz at distances to ~200 km—a unique window into earthquake source dynamics. Combined seismic and hydrophone observations show that the traditional T wave propagates as a seismoacoustic polarized interface wave “Ti” coupled to the seafloor. Seismoacoustic Ti waves propagating at the sound speed of water are routinely observed over megameter distances at H2O between Hawaii and California, even though the seafloor site is within the shadow zone for acoustic wave propagation. Internal waves or thermohaline covariation may or may not be sufficient to scatter acoustic energy from the SOFAR channel to the deep seafloor. Ti has also been observed on seismometers SSW of Oahu at the OSN1 site at the seafloor and within an ODP borehole 242 m into the basalt basement. The observation of Ti from an earthquake in Guatemala at OSN1, whose path is blocked by the Island of Hawaii, is consistent with scattering from the vicinity of the Cross Seamount.

Spatio-Temporal Patterns of Beaked Whale Echolocation Signals in the North Pacific

At least ten species of beaked whales inhabit the North Pacific, but little is known about their abundance, ecology, and behavior, as they are elusive and difficult to distinguish visually at sea. Six of these species produce known species-specific frequency modulated (FM) echolocation pulses: Baird’s, Blainville’s, Cuvier’s, Deraniyagala’s, Longman’s, and Stejneger’s beaked whales. Additionally, one described FM pulse (BWC) from Cross Seamount, Hawai’i, and three unknown FM pulse types (BW40, BW43, BW70) have been identified from almost 11 cumulative years of autonomous recordings at 24 sites throughout the North Pacific. Most sites had a dominant FM pulse type with other types being either absent or limited. There was not a strong seasonal influence on the occurrence of these signals at any site, but longer time series may reveal smaller, consistent fluctuations. Only the species producing BWC signals, detected throughout the Pacific Islands region, consistently showed a diel cycle with nocturnal foraging. By comparing stranding and sighting information with acoustic findings, we hypothesize that BWC signals are produced by ginkgo-toothed beaked whales. BW43 signal encounters were restricted to Southern California and may be produced by Perrin’s beaked whale, known only from Californian waters. BW70 signals were detected in the southern Gulf of California, which is prime habitat for Pygmy beaked whales. Hubb’s beaked whale may have produced the BW40 signals encountered off central and southern California; however, these signals were also recorded off Pearl and Hermes Reef and Wake Atoll, which are well south of their known range.

A new species and record of Serpulidae (Annelida: Polychaeta) from Cross Seamount in the Hawaiian Chain

A new species and record of Serpulidae (Annelida: Polychaeta) from Cross Seamount in the Hawaiian Chain

Nursery origin of yellowfin tuna in the Hawaiian Islands

Stable isotopes of carbon (! 13 C) and oxygen (! 18 O) in otolith cores (first 2 mo of age) of young-of-the-year (YOY) yellowfin tuna Thunnus albacares were used as natural tracers to pre- dict the nursery origin of sub-adults (age-1) collected from the Hawaiian Islands. YOY fish were first collected from nurseries throughout the western and central Pacific Ocean (WCPO) to deter- mine whether ! 13 C and ! 18 O values of otolith cores (! 13 Cotolith and ! 18 Ootolith) were sufficiently dif- ferent to discriminate individuals from different nurseries used during the YOY period. Nurseries examined included both nearshore Hawaiian Islands and offshore Hawaiian Islands (Cross Seamount), and 4 locations in the equatorial Pacific Ocean: Line Islands, Marshall Islands, Solomon Islands, and Philippines. Significant differences existed in ! 13 Cotolith and ! 18 Ootolith among YOY yellowfin tuna from different nurseries for each year of the 2 yr study period (2008!2009). Individuals from the nearshore Hawaiian Islands were most enriched in ! 18 Ootolith, while samples obtained from the Philippines were most depleted in both ! 13 Cotolith and ! 18 Ootolith relative to other regions. Inter-annual variability in otolith core chemistry was minor and only observed for individ- uals collected from the Philippines. Overall classification success from quadratic discriminant function analysis of YOY yellowfin tuna to their respective nursery of collection was 63 and 87% for 2008 and 2009, respectively. Mixed-stock analysis indicated 91% of the sub-adult yellowfin tuna collected from the nearshore Hawaiian Islands originated from this same nursery. In addition, sub-adults from the offshore location within the Hawaiian Islands appear to originate from the nearshore Hawaiian Islands, highlighting the importance of local production and retention of yellowfin tuna to the standing stock and domestic fisheries of Hawaii.

A new species and record of Serpulidae (Annelida: Polychaeta) from Cross Seamount in the Hawaiian Chain

A new species of the serpulid genus Metavermilia Bush, 1905 and a new record of the genus Omphalopomopsis Saint-Joseph, 1894 are described from deep-sea lava rocks collected from 2,013 m at Cross Seamount, southwest of the Hawaiiarchipelago. Metavermilia zibrowii sp. nov., differs from its congeners mostly by the presence of a simple and concaveoperculum, extent of the thoracic membrane and tube morphology. Omphalopomopsis langerhansii (Marenzeller, 1885)is the type species of the genus and it is only known through its type specimen. This species is characterized by a simpleoperculum with a shallow convex calcareous endplate, cylindrical peduncle, presence of Apomatus chaetae and high num-ber of teeth in the thoracic uncini. This is the first record of this species outside the type locality and both genera are newly recorded for the Hawaiian Islands.

Micronekton abundance and biomass in Hawaiian waters as influenced by seamounts, eddies, and the moon

Micronekton abundance, biomass, and community composition was determined from 58 Cobb trawl samples taken from 2005 to 2008 at several locations in the lee of the Hawaiian Islands. The results indicated a strong influence of the lunar illumination on micronekton abundance and biomass. This effect was evident in shallow night tows and probably was the result of lunar light affecting the nighttime depths of migrating species. The abundance and biomass of micronekton is remarkably consistent between years and areas in Hawaiian waters after the affects of moon phase are accounted for. Micronekton, principally migratory myctophids, were reduced over the summit of Cross Seamount but not Finch Seamount that has a summit below the daytime depth of most migrators. However, during a new moon, micronekton abundance over Cross seamount was similar to surrounding areas either because of altered migration patterns or because predators such as tunas cannot forage as effectively at night without lunar illumination. Species belonging to the Hawaiian mesopelagic boundary layer community were found to vary in presence and abundance between years at Cross Seamount suggesting that a consistent seamount associated fauna does not exist. Sparse sampling of a cyclonic mid-ocean eddy suggested very high micronekton abundance and biomass both in shallow waters at night but also at depth during the day. Although preliminary, these results suggest that eddies may aggregate the micronekton which probably feed on the enhanced secondary productivity.

Echolocation signals of a beaked whale at Palmyra Atoll

Acoustic recordings from Palmyra Atoll, northern Line Islands, central Pacific, showed upsweep frequency modulated pulses reminiscent of those produced by beaked whales. These signals had higher frequencies, broader bandwidths, longer pulse durations and shorter inter-pulse intervals than previously described pulses of Blainville's, Cuvier's and Gervais' beaked whales [Zimmer et al. (2005). J. Acoust. Soc. Am. 117, 3919-3927; Johnson et al. (2006). J. Exp. Biol. 209, 5038-5050; Gillespie et al. (2009). J. Acoust. Soc. Am. 125, 3428-3433]. They were distinctly different temporally and spectrally from the unknown beaked whale at Cross Seamount, HI [McDonald et al. (2009). J. Acoust. Soc. Am. 125, 624-627]. Genetics on beaked whale specimens found at Palmyra Atoll suggest the presence of a poorly known beaked whale species. Mesoplodon sp. might be the source of the FM pulses described in this paper. The Palmyra Atoll FM pulse peak frequency was at 44 kHz with a -10 dB bandwidth of 26 kHz. Mean pulse duration was 355 mus and inter-pulse interval was 225 ms, with a bimodal distribution. Buzz sequences were detected with inter-pulse intervals below 20 ms and unmodulated spectra, with about 20 dB lower amplitude than prior FM pulses. These clicks had a 39 kHz bandwidth (-10 dB), peak frequency at 37 kHz, click duration 155 mus, and inter-click interval between 4 and 10 ms.

An acoustic survey of beaked whales at Cross Seamount near Hawaii

An acoustic record from Cross Seamount, southwest of Hawaii, revealed sounds characteristic of beaked whale echolocation at the same relative abundance year-around (270 of 356 days), occurring almost entirely at night. The most common sound had a linear frequency upsweep from 35 to 100 kHz (the bandwidth of recording), an interpulse interval of 0.11 s, and duration of at least 932 mus. A less common upsweep sound with shorter interpulse interval and slower sweep rate was also present. Sounds matching Cuvier's beaked whale were not detected, and Blainville's beaked whale sounds were detected on only one occasion.

The influence of a Hawaiian seamount on mesopelagic micronekton

The distribution of mesopelagic micronekton (small fishes, crustaceans, and cephalopods) is not uniform throughout the oceans. Seamounts are a feature that may influence the abundance, biomass, diversity, and taxonomic composition of a community of mesopelagic micronekton by introducing a hard substrate and benthic predators into a realm normally devoid of these. Cross Seamount, located roughly 295 km south of the island of Oahu, Hawaii, has a summit that is 330 m below sea surface and has a diameter of approximately 8 km. Using a large, modified Cobb trawl, samples were taken both directly over and away from the summit of Cross Seamount to sample the deep scattering layer during the day and the shallow scattering layer during the night. Trawls were conducted during two cruises in the spring of 2005 and 2007. All organisms collected were identified to the lowest taxonomic level possible resulting in a description of the local assemblage of mesopelagic micronekton over and around Cross Seamount. Results indicate that there is a significant decrease in total abundance of organisms and an absence of certain diel vertically migrating taxa directly over the summit as opposed to away. While predation might be partly the cause, the taxa that are absent from the summit all have daytime depths that are deeper than the depth of the summit indicating that avoidance may be a major reason for the low abundance. The overall taxonomic composition of the community over the summit is dominated numerically by epipelagic juvenile fishes and stomatopod larvae. This is in opposition to that found away from the summit where the community is dominated numerically by mesopelagic fishes, mostly myctophid fishes, with the epipelagic juvenile fishes and stomatopod larvae contributing little to the overall taxonomic composition. The community over the summit also contains two species that appear to be found in higher abundance over the summit as opposed to away and may be considered as seamount-associated species. These are a cranchiid squid, Liocranchia reinhardti, and a myctophid fish, Benthosema fibulatum. This seamount is known to impact the mesopelagic micronekton community and tuna community, but the mechanisms behind these impacts are largely unknown at this time.

Temporal patterns in the acoustic signals of beaked whales at Cross Seamount

Seamounts may influence the distribution of marine mammals through a combination of increased ocean mixing, enhanced local productivity and greater prey availability. To study the effects of seamounts on the presence and acoustic behaviour of cetaceans, we deployed a high-frequency acoustic recording package on the summit of Cross Seamount during April through October 2005. The most frequently detected cetacean vocalizations were echolocation sounds similar to those produced by ziphiid and mesoplodont beaked whales together with buzz-type signals consistent with prey-capture attempts. Beaked whale signals occurred almost entirely at night throughout the six-month deployment. Measurements of prey presence with a Simrad EK-60 fisheries acoustics echo sounder indicate that Cross Seamount may enhance local productivity in near-surface waters. Concentrations of micronekton were aggregated over the seamount in near-surface waters at night, and dense concentrations of nekton were detected across the surface of the summit. Our results suggest that seamounts may provide enhanced foraging opportunities for beaked whales during the night through a combination of increased productivity, vertical migrations by micronekton and local retention of prey. Furthermore, the summit of the seamount may act as a barrier against which whales concentrate prey.

Observations of polarized seismoacoustic T waves at and beneath the seafloor in the abyssal Pacific ocean

Combined seismic and hydrophone observations show that the traditional T wave propagates as a seismoacoustic polarized interface wave (Ti) coupled to the seafloor. Seismoacoustic Ti waves propagating at the sound speed of water are routinely observed over megameter distances at the deep (4979 m) seafloor Hawaii-2 Observatory (H2O) between Hawaii and California, even though the seafloor site is within a shadow zone for acoustic wave propagation. Ti has also been observed on seismometers 225 km SSW of Oahu at the OSN1 site at the seafloor and within an ODP borehole into the basalt basement. Analyses of timing, apparent velocity, energy, and polarization of these interface waves are presented. At low frequency (< approximately 5 Hz) Ti propagates dominantly in the sediments and is consistent with higher-mode Rayleigh waves. At higher frequencies the observed Ti waves dominantly propagate acoustically with characteristics suggesting local scattering. The observation of Ti from an earthquake in Guatemala at OSN1, whose path is blocked by the Island of Hawaii, is consistent with scattering from the vicinity of the Cross Seamount.

Distribution of recent volcanism and the morphology of seamounts and ridges in the GLIMPSE study area: Implications for the lithospheric cracking hypothesis for the origin of intraplate, non–hot spot volcanic chains

Lithospheric cracking by remotely applied stresses or thermoelastic stresses has been suggested to be the mechanism responsible for the formation of intraplate volcanic ridges in the Pacific that clearly do not form above fixed hot spots. As part of the Gravity Lineations Intraplate Melting Petrology and Seismic Expedition (GLIMPSE) project designed to investigate the origin of these features, we have mapped two volcanic chains that are actively forming to the west of the East Pacific Rise using multibeam echo sounding and side‐scan sonar. Side‐scan sonar reveals the distribution of rough seafloor corresponding to recent, unsedimented lava flows. In the Hotu Matua volcanic complex, recent flows and volcanic edifices are distributed over a region 450 km long and up to 65 km wide, with an apparent, irregular age progression from older flows in the west to younger in the east. The 550‐km‐long Southern Cross Seamount/Sojourn Ridge/Brown Ridge chain appears to have been recently active only at its eastern end near the East Pacific Rise. A third region of recent flows is found 120 km north of Southern Cross Seamount in seafloor approximately 9 Myr old. No indication of lithospheric extension in the form of faulting or graben formation paralleling the trend of the volcanic chains is found in the vicinity of recent flows or anywhere else in the study area. Thermoelastic cracking could be a factor in the formation of a few small, very narrow volcanic ridges, but most of the volcanic activity is broadly distributed in wide swaths with no indication of formation along narrow cracks. The Sojourn and Brown chains appear to begin as distributed zones of small seamounts that later develop into segmented ridges, perhaps under the influence of membrane stresses from self‐loading. We suggest that the linear volcanic chains are created by moving melting anomalies in the asthenosphere and that lithospheric cracking plays at most a secondary role.

Analysis of gravity and topography in the GLIMPSE study region: Isostatic compensation and uplift of the Sojourn and Hotu Matua Ridge systems

The Gravity Lineations Intraplate Melting Petrologic and Seismic Expedition (GLIMPSE) Experiment investigated the formation of a series of non–hot spot, intraplate volcanic ridges in the South Pacific and their relationship to cross‐grain gravity lineaments detected by satellite altimetry. Using shipboard gravity measurements and a simple model of surface loading of a thin elastic plate, we estimate effective elastic thicknesses ranging from ∼2 km beneath the Sojourn Ridge to a maximum of 10 km beneath the Southern Cross Seamount. These elastic thicknesses are lower than predicted for the 3–9 Ma seafloor on which the volcanoes lie, perhaps due to reheating and thinning of the plate during emplacement. Anomalously low apparent densities estimated for the Matua and Southern Cross seamounts of 2050 and 2250 kg m−3, respectively, probably are artifacts caused by the assumption of only surface loading, ignoring the presence of subsurface loading in the form of underplated crust and/or low‐density mantle. Using satellite free‐air gravity and shipboard bathymetry, we calculate the age‐detrended, residual mantle Bouguer anomaly (rMBA). The rMBA corrects the free‐air anomaly for the direct effects of topography, including the thickening of the crust beneath the seamounts and volcanic ridges due to surface loading of the volcanic edifices. There are broad, negative rMBA anomalies along the Sojourn and Brown ridges and the Hotu Matua seamount chain that extend nearly to the East Pacific Rise. These negative rMBA anomalies connect to negative free‐air anomalies in the western part of the study area that have been recognized previously as the beginnings of the cross‐grain gravity lineaments. Subtracting the topographic effects of surface loading by the ridges and seamounts from the observed topography reveals that the ridges are built on broad bands of anomalously elevated seafloor. This swell topography and the negative rMBA anomalies contradict the predictions of lithospheric cracking models for the origin of gravity lineaments and associated volcanic ridges, favoring models with a dynamic mantle component such as small‐scale convection or channelized asthenospheric return flow.

Vertical movements of bigeye tuna (Thunnus obesus) associated with islands, buoys, and seamounts near the main Hawaiian Islands from archival tagging data

AbstractTo learn more about the movement patterns of bigeye tuna (Thunnus obesus), we deployed archival tags on 87 fish ranging in fork length from 50 to 154 cm. Thirteen fish were recaptured, from which 11 archival tags were returned, representing in aggregate 943 days‐at‐liberty. We successfully retrieved data from 10 tags, representing 474 days in aggregate. The largest fish recaptured was 44.5 kg [131 cm fork length (FL)] and the smallest 2.8 kg (52 cm). The deepest descent recorded was 817 m, the coldest temperature visited 4.7°C, and minimum oxygen level reached ∼1 mL L−1. Fish spent little time at depths where water temperatures were below 7°C and oxygen levels less than ∼2 mL L−1. Five fish were recaptured near the offshore weather buoy where they were tagged. Based on vertical movement patterns, it appeared that all stayed immediately associated with the buoy for up to 34 days. During this time they remained primarily in the uniform temperature surface layer (i.e. above 100 m). In contrast, fish not associated with a floating object showed the W‐shaped vertical movement patterns during the day characteristic of bigeye tuna (i.e. descending to ∼300–500 m and then returning regularly to the surface layer). Four fish were tagged and subsequently recaptured near Cross Seamount up to 76 days later. These fish exhibited vertical movement patterns similar to, but less regular than, those of fish not associated with any structure. Bigeye tuna appear to follow the diel vertical movements of the deep sound scattering layer (SSL) organisms and thus to exploit them effectively as a prey resource. Average night‐time depth was correlated with lunar illumination, a behaviour which mimics movements of the SSL.

Exchange rates of yellowfin and bigeye tunas and fishery interaction between Cross seamount and near-shore FADs in Hawaii

Yellowfin and bigeye tunas ( Thunnus albacores and Thunnus obesus) were tagged and released between August 1995 and December 1997 at Cross Seamount and NOAA weather buoys about 200 Nmi south of Honolulu. The release and recapture data were stratified into five sites, and a bulk transfer model was used to estimate natural mortality, fishing mortality and transfer rates between the five sites. Bigeye are much more persistent at Cross seamount and less vulnerable to the fishery than yellowfin. Fishing accounts for about 5 % of the total mortality of both bigeye and yellowfin at Cross Seamount. Yellowfin are a major component of catches at inshore FADs in Hawaii. The rate of immigration from Cross Seamount to the inshore FADs is very low for both species. The fishing mortality at Cross seamount is substantial but is not adversely impacting the populations either at Cross or the inshore FADs.

Temporal variations in the deep-water colonization rates of small benthic foraminifera: the results of an experiment on Cross Seamount

Modern benthic foraminifera are important remineralizers of organic matter and a link between surface-ocean production and life in the deep sea. Assemblages of benthic foraminifera are preserved in the fossil record, providing clues to paleoceanographic conditions. These clues can be fully interpreted only when our knowledge of the biology and ecology of modern species is more complete. To study factors influencing foraminiferal colonization rates, artificial substrates were placed on Cross Seamount (18°40′N, 158°17′W) for 1 to 42 months between 1989 and 1994. The colonization rates of benthic foraminifera onto different substrates (five mineral types were used) at four water depths (800, 975, 1285 and 2000 m) were determined. Both calcareous and agglutinated foraminifera inhabited these artificial substrates at different rates. Many of the agglutinated forms colonized at a uniform rate through time. The colonization rates of other foraminifera, primarily calcareous forms, were not constant through time, nor could the variability be attributed to the controlled variables (water depth and substrate composition). Instead, these temporal variations in colonization rate corresponded with shifts in surface ocean conditions and export fluxes in the central Pacific. Other ecological observations are also presented, including size- and spatial-distributions.