Pacific Science (1995), vol. 49, no. 2: 143-155 © 1995 by University of Hawai'i Press. All rights reserved Aspects of the Natural History of Pelagic Cephalopods of the Hawaiian Mesopelagic-Boundary Region 1 RICHARD EDWARD YOUNG 2 ABSTRACT: Pelagic cephalopods of the mesopelagic-boundary region in Hawai'i have proven difficult to sample but seem to occupy a variety ofhabitats within this zone. Abralia trigonura Berry inhabits the zone only as adults; A. astrosticta Berry may inhabit the inner boundary zone, and Pterygioteuthis giardi Fischer appears to be a facultative inhabitant. Three other mesopelagic species, Liocranchia reinhardti (Steenstrup), Chiroteuthis imperator Chun, and Iridoteuthis iris (Berry), are probable inhabitants; the latter two are suspected to be nonvertical migrants. The mesopelagic-boundary region also contains a variety of other pelagic cephalopods. Some are transients, common species of the mesopelagic zone in offshore waters such as Abraliopsis spp., neritic species such as Euprymna scolopes Berry, and oceanic epipelagic species such as Tremoctopus violaceus Chiaie and Argonauta argo Linnaeus. Others are appar­ ently permanent but either epipelagic (Onychoteuthis sp. C) or demersal (No­ totodarus hawaiiensis [Berry] and Haliphron atlanticus Steenstrup). Submersible observations show that Nototodarus hawaiiensis commonly "sits" on the bot­ tom and Haliphron atlanticus broods its young in the manner of some pelagic octopods. THE CONCEPT OF the mesopelagic-boundary over bottom depths of the same range. The region (m-b region) was first introduced by designation of an inner zone is based on Reid et al. (1991), although a general asso­ Reid'sfinding mesopelagic fishes resident there ciation of various mesopelagic animals with during both the day and night; mesopelagic land masses has been known for some time. fishes are virtually absent at these daytime They defined the horizontal and vertical lim­ depths in waters seaward of the boundary its of the daytime zone in Hawai'i waters as zone. At least two species of boundary ani­ depths of 400-700 m that occur above bot­ mals in Japan, the squid Watasenia scintillans tom depths of the same range. Recently S. B. (Berry), and the shrimp Sergia lucens (Han­ Reid (unpubl. data) has found that the zone sen), undergo daily horizontal migrations to­ is more extensive than originally thought; the ward and away from shore (Sasaki 1914, m-b region now includes the former boun­ Omori and Ohta 1981). Reid (unpubl. data) dary region, now termed the "outer mesope­ found some evidence for similar migrations lagic-boundary zone" (outer m-b zone), and in Hawaiian boundary lantemfishes (mycto­ a new zone, the "inner mesopelagic-boun­ phids). dary zone" (inner m-b zone). The latter is Knowledge of the species composition, defined as depths of ca. 250-400 m that lie distribution, and movements of the pelagic fauna of the boundary region in general is poor, and for cephalopods it is almost non­ existent. This paper reports on the ceph­ 1 This work was supported in part by Grant No. alopods taken during an extensive sampling 0CE900206-frOln-th1:-Nmional-Science Founaafion ana program in Hawanan waters and draws on a grant from the Hawai'i Undersea Research Labo­ ratory. Manuscript accepted 9 May 1994. data from other studies in this region to 2 Department of Oceanography, University of Hawai'i summarize our present understanding of the at Manoa, Honolulu, Hawai'i 96822. boundary region's cephalopod fauna. 143 144 PACIFIC SCIENCE, Volume 49, April 1995 TABLE 1 SUMMARY OF TRAWLING EFFORT BY THE THREE PROGRAMS PARAMETER UH:IKMf DR: NEUSTON NMFS Hokusei Maru Net mouth, m2 40 1.6 100 200 Time Mostly night Night Night Twilight-night Maximum depth Mostly 200 m Surface 147 m 250m Tow duration 1.5 hr Uhr 2hr 2hr Inner m-b tows 163 142 2+ 0 Outer m-b tows 147 171 2- 7 2 MATERIALS AND METHODS m . All sampling involved the use of open nets and most tows were taken at night. S. B. Most squids were captured during three Reid will provide details of the UH sampling trawling programs: (l) A series of seven tows program in a forthcoming paper. Most IK taken from the FTS Hokusei Maru (HM) samples in that series were oblique tows from with a commercial-size net having a mouth 2 o to 200 m, but shallower tows (0 to 50-75 opening ofca. 200 m (graded mesh, 400 mm m) were necessary when bottom depth was to 14 mm stretch). These tows fished from 100 m and at the edge of Penguin Bank (0­ 250 to 0 m at a speed of ca. 1.5 cm/sec dur­ 100 m), where shallow pinnacles mad~ stan­ ing twilight from 1800 hours to 2000 h0':lrs dard trawling hazardous. A few honzontal local time. Data from the HM tows and In­ 2 and daytime tows were also taken. We sam- cidental data taken with either a 8-m mouth ~he 2 .pled during regular time periods during Isaacs-Kidd (IK) trawl or a 40-m mouth night and just before sunset and after sunnse. rectangular trawl have been reported pre­ Most tows were taken over bottom depths of viously (Reid et al. 1991). All of the HM 700 m or less and at speeds of 1.75-2.0 m/ tows were taken in the outer m-b zone. (2) A sec. The number of tows was approximately·· series of four tows taken from the RlV evenly split between the inner m-b zone and Townsend Cromwell, National Marine Fish­ the outer m-b zone. Neuston tows were taken eries Service (NMFS), with a pelagic rope concurrently with the IK samples. The traw!­ trawl with a 100-m 2 mouth (graded mesh, ing data are summarized in Table 1: In addi­ 292 mm to 19 mm stretch). These were open tion to trawling, visual observatIOns and stratified oblique tows to a maximum depth video recordings of boundary animals were of 147 m that fished primarily between 50 made during three dives with the University and 100 m. Two of these tows, taken off lee­ of Hawai'i submersible Pisces V during the ward O'ahu, fished parallel to the coast along daytime off leeward Liina'i over bottom a steep slope. Bottom depths there drop from depths of 250-600 m. 100 to 400 m over a horizontal distance of about 1 km. Two tows, taken off windward O'ahu, fished orthogonal to the coast over RESULTS bottom depths of ca. 100-1000 m. Therefore, two tows fished the inner m-b zone, and two Abralia trigonura Berry tows passed through the inner and outer m-b zones and terminated in more oceanic waters. The largest catches of A. trigonura were (3) A series of 633 tows taken from the R/V made by the large HM trawl. The maximum Moana Wave, University ofHawai'i ruB ser- catch was 787 squid, and catches exceeded ies), approximately evenly split between those 100 individuals in all seven tows (Reid et al. with a 7-m IK with a 40-m2 mouth (graded 1991). Measurements were made from a rep­ mesh, 200 to 3 mm stretch) and a 2-m neu­ resentative sample of 1439 A. trigonura taken ston trawl with an effective mouth area of 1.6 by HM trawls; of these 45% were mature ,-,.fQfi'ii&kdf a; iiri4~&htWMffl!!.W'@Wt':;,*,iW1W?m,:!U#¥ ¥@ HP>li!ii& Pelagic Cephalopods in the Mesopelagic-Boundary Region-YoUNG 145 100 90 Mature males 80 ._ ....-..... ..... ...... • 70 .. -............... Mature I 0 females () 60 I-« () 50 Immature l.I.. ~ males 0 40 ~ 0 30 ~ Immature 20 females 10 0 HOK. MARU NMFS IK Neuston UH FIGURE I. Comparison ofcatches ofvarious stages of Abralia trigonura from the different sampling programs and different trawls. HOK. MARU, Hokusei Maru 200-m2 trawl; NMFS, National Marine Fisheries Service IOO-m 2 rope trawl; UH, University of Hawai'i, IK, 40-m2 trawl, Neuston, 1.6-m2 trawl. males, 41 % mature females, 2% immature Penguin Bank captured only one A. trigonura males, and 12% immature females (Figure 1). and one P. giardi Fischer and seven oceanics. The NMFS series captured 817 A. trigonura, That locality has maximum bottom depths of of which 739 were examined; of these, 69% around 300 m but lies next to a steep drop-off were mature males, 8% mature females, 1% that reaches depths of > 1000 m and is fre­ immature males, and 22% immature females. quently swept by strong tidal currents. The DR series with the IK captured 217 A. Excluding catches over the Penguin Bank trigonura outside the Penguin Bank region region, A. trigonura was most abundant in (see below); ofthese, 54% were mature males, the DR series over bottoms of 450-650 m. 24% mature females, 4% immature males, Only a few captures of A. trigonura were and 18% immature females. The DR neuston made over average bottom depths of < 350 trawl series caught 25 A. trigonura; of these, m (Figure 2). In contrast, the most successful 24 (96%) were mature females and one was a of the four NMFS tows (station 29; 563 A. mature male. trigonura captured) was taken over bottom The data from all trawling series show depths of 110-283 m along a steep slope that immature squids are not being effectively (leeward O'ahu). Catch rates in the DR study sampled by any of these nets. Overall, only were very poor relative to those taken in the 4.4% of the catch from all trawl series con­ other series. The average catch of this species sisted of squids < 25 mm mantle length in the DR series was 1.1 squid per tow (range, (ML).