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The factors contributing to similarities and differences found in the species composition between two IKMT’s Research Paper



Four series of oblique tows were taken with a midwater trawl in the San Pedro and Santa Catalina Basins off Southern California. Comparisons of biomass, numbers, and mean sizes of fish and decapod crustaceans between day and night tows show few significant differences, indicating that daytime net avoidance is not a problem with this sampling method.

Day to night differences in numbers of individuals captured were greater in Catalina than in San Pedro Basin, as was variability from trawl to trawl in overall species numbers. Rank order of abundance appears to be a relatively predictable community characteristic for the common species of fish and decapods captured.

Ecologists have been moderately successful in describing and quantifying temporal and spatial patterns of distribution for organisms living in terrestrial ecosystems. In the pelagic marine environment sampling is complicated because the investigator usually cannot see the actual sampling area and the water masses are in motion relative to the sampler.

Success in understanding distributional patterns has been greater for shallow water organisms than for midwater organisms. Quantitative sampling studies of the mid- waters have been relatively few and have involved monthly or seasonal studies at selected depths without replication. The need for replication has been emphasized by the studies of which have indicated that most species of fishes have a highly clumped distribution.

This paper is discussing the outcomes of the experiments carried out as part of a field studies class, which calls for individual gathering of information in the field. In this case, the field study required one to go on an Isaac Kidd Midwater Trawl trip. Isaac Kidd Midwater Trawl is a form of sampling data regarding pelagic organisms in the ocean.

This study made use of 100 samples found in the San Pedro Basin. The equipments in use included a well-equipped boat and a large net. The first study was on September 28th where several experiments on neuston nets and trawls were carried out. On this day, at around 5.00pm we performed a 100m day neuston tow followed by 100m neuston tow at 7.30pm.

Another trawl took place at 3.15pm-750m day trawl and the next one at 7.00pm-850m night trawl closing the studies of September 28. On this day of September 28, there were clear skies with a high temperature of 77F and a low of 65F. The sunset was at 6.20pm, and the ocean was calm hence allowing the study to take place smoothly.

The second study was on December 2 where we also performed four trawls. the first one was at 3.30pm- 100m day neuston tow, night neuston tow of 100m at 6.05pm, 400m day trawl at 3.55pm and the last one was at 6.28pm-400m night trawl. On this day, the high was at 66F and a low of 47F.

The weather was cold and exceptionally windy all day long. On this particular day, there was a large swell and the sunset took place at 4.44pm. This early sunset reduced the amount of daylight, which was to be compared to the first study. The composition of the species in the study was of 100m depth, and these included substantial groups like copepod, larvae, protozoan, krill, pteropod, meroplankton, salps, and chaetognatha.

There was an outstanding group of Mesopelagic whose composition are copepods, krill, shrimp, arrow worms, squid, and lantern fish and bristle mouth. In comparing the samples of any study, there should be species diversity because of varied breeding seasons and changes in seasonality (Christopher and Lowe 67).


In research, information can be from primary or secondary sources. Primary sources of information involve first hand information obtained using interviews, questionnaires, and observation. The information provided in this paper in majorly from primary sources of information through observation.

The process of collecting information involved sampling off southern California Coast using IKMT net day and night and then observing the outcomes of the activities. In addition, there was the neuston net, which also took place at day and night, and lastly comparing the results of the activities of two days. The study of September 28 was a pelagic trip, and one, which took place, on December 2, was a marine trip.

Four series of repeated tows were taken during the beginning and end of autumn with an Isaacs and Kidd midwater trawl (IKMT) aboard the Yellow fin from the Southern California Marine Institute. The building was a long line, baits boat, and had transformation for oceanographic research by the Ocean Studies Institute in 1987.

This vessel is all aluminum, transom stern, twin diesel with a semi-planning hull (SCMI.us). The following aspects of epipelagic and mesopelagic communities off San Pedro, Ca are investigated regarding differences in abundance and diversity between night and day trawls and variability in species affinities between the trawls.

In our Pelagic Organisms laboratory all species were identified and counted that pertained to the IKMT performed on September 28, 2011.


In this part of the paper, we present the results of the four activities comparing and contrasting their outcomes. On the first day, where we made use of 100m trawl the pelagic present were euphausida, decapods, squid, thaliacea, and chaetognatha. The common ones were copepod, ctenophora, and siphonophora.

In the marine, we had crab and isopods. the night trawl had the following pelagic- Euphausida, decapods, my sid, arrow worm, larvae, bristle mouth, flatfish, squid, sea butterfly, salp, bract, lantern fish, smooth tongue, comb jelly, and hatchet fish. The common ones in the night trawl were siphonophora and copepod while, on the marine part, we had isopod and sea gooseberry.

Comparing the day mesopelagic trawl we had the following outcomes- under pelagic we had CA slick head, lamp fish, black dragon, CA headlight fish, beroe, hydromedusae, and pteropod. The common ones under this category include octopus, sea gooseberry, flatfish, and silvery hatchet fish, and showy bristle mouth, pyrosoma, at olla, siphonophore, and chaetognatha. In the marine part, we have mysid, decapods, and amphipods (Fenchel 71).

Comparing night mesopelagic trawls, the studies had the following outcomes. Under pelagic, we had ostracoda, arrow worm, annelid, black smelt, and blenny. the common outcomes in the two studies which took place at night, we had Krill, my sid, salps, at olla, decapoda, beroe, flatfish, squid, black belly dragon, black dragon fish, copepod, crested monumental scale, bent tooth bristle mouth, siphonophora, chaetognatha, and midwater eelpout.

The marine category had paraphrinima, pipefish, smooth tongue fish, pyrosoma, and periphylia. In comparing the above outcomes, we drew up conclusions on what the results indicated. The study, which had 100m we had pelagic IKMT of approximately twenty five species while marine IKMT had algae and other eight species. The night session recorded pelagic IKMT of approximately 31 species, and marine IKMT of roughly ten species.

Under the category, of mesopelagic we recorded approximately pelagic IKMT-32species and marine IKMT-22 species during the day. In the night, we had a record of pelagic IKMT-37 species, and marine- 29 species. These results had similarities and differences on the two days that the activities were carried out. In the next part of this paper, we discuss in detail these similarities, differences, and the reasons for their occurrences (Mittelbach 84).

Comparisons of daytime and night-time tows were made for volume dis-placement biomass, mean size and mean number of individuals, and mean number of species in the Pelagic IKMT.

“The relatively high similarity from trawl to trawl in total density of fish and decapods may be an indication that the habitat is placing limits on the overall density. Food is generally recognized as an important limiting factor in the deep sea. If food is also an important factor in limiting overall density in the midwaters, the variability in relative density recorded here for individual species of fish may be related in part to the feeding habits of the common species of fish, which are generalized plankton feeders”

“The decapod data, however, suggest a possible relationship between total decapod abundance and the relative abundance of Sergestes, sitnilis, and Hqrmenotr’ora frontah. The results indicate that variability in sampling technique from trawl to trawl is not responsible for the observed variability in abundance”.

Compare Day one- 100m Trawl

Pelagic Common Marine

Compare night 100m Trawl

Pelagic Common Marine
Arrow worm
Hatchet fish
Bristle mouth
Smooth tongue
Lamp fish
Lantern fish
Flat fish
Comb Jelly
Sea Butterfly
Sea goosberry

Compare Day Mesopelagic Trawl

Pelagic Common Marine
CA slick head
CA head lightfish
Black Dragon
Lamp fish
Silvery Hatchet fish
Benttooth Bristle mouth
Showy Bristlemouth
Flat fish
Sea Goosberry
Crested Big Scale Fish

Compare Night Mesopelagic Trawl

Pelagic Common Marine
Arrow Worm
Silvery Hatchet fish
Flat fish
Black Dragon fish
Bent tooth Bristle mouth
Crested Bigscale
Black Belly Dragon
Pipe fish
Smooth Tongue Fish

Multi-species aggregations may be patchy with regard to density or with regard to Species type. These results indicate that over most of the area sampled the relative abundance of the common species of fish and decapods is a consistent feature of the community.


Some species are present during the day and not observed when the activity is taking place at night. That aside there is the species, which are present in both times, and on the two days, the study took place. The differences in the results of the study were due to various reasons both physical and biological.

The second experiment there was a variance in the circumstances under which the observations took place starting from exposure to daylight to temperatures of the place. One of the utmost, notable reasons for the difference in the observed samples is the weather of the basin. The first day of September 28 had relatively higher temperatures than the second day.

The temperatures on the first day were ranging from 77F to 65F, which is extremely hot. Some species will thrive under such temperatures while others will do well in colder temperatures. This can be the reason why we observed some species on day one and not on the second day. The ocean on September 28 was calm and the day had a longer exposure to daylight with the sun setting at 6.28pm.

When it comes to aquatic animals, their existence is subject to various factors, which are the reasons for the difference in the above studies. Some species will exist in waters, which have lighter, calm waters, high temperatures, and presence of swell. There are those species, which will thrive in conditions, which are totally opposite to the above mention ones. The major impact these factors have on the species is its compositions.

The presence or absence of the above factors will cause significant changes in species composition within the two IKMT’s. Hypothetically, the difference in outcomes is because of collecting data at varied temperatures, different depths, seasonality, and presence of a swell. Sampling of data took place almost two months apart, which can mean a difference in the seasons of the ocean.

During the sampling of data on the second day-, December 2 there was less sunlight available because of the early sunset, which was at 4.44pm. This means that the sampling that was done after 4.44pm was in total darkness and, therefore, affected the night trawl that took place an hour after sunset.

How did this affect the results? The presence of darkness while sampling on the second day could have an effect on the species in relation to organisms that vertically migrate with the presence of the sun and those which survive in darkness. In this case, the species, which migrate, in daylight disappear when darkness appears and, therefore, the sampling will only include those organisms, which can survive in darkness.

In this case, the amount of darkness or lack of sunlight will decide the vertical location of organisms in the area the sampling will be taking place. The presence of sunlight or its absence is the significant reason for the variation of species composition. This will be due to the organisms being found closer to the surface in order to be closer to the sunlight.

This bears importance because on the surface, there is a significant amount of sunlight and these organisms will survive best in these conditions. In turn, this can determine their relative vertical position in relation to the depth of the ocean waters.

In terms of the water depth, it is evident that the species found normally at deeper ends would be present near the surface earlier in the day as they seek for sunlight. The moment the sunrays hit the water surface these species will move closer to the surface in a response to the light from the sun.

The opposite will happen to the sampling that took place on September 28 during the night. On this day, the sampling of night trawls took place after sunset meaning that the organisms, which exist in sunlight would have left the water surface. The presence of the organisms, which responds to the light from the sun, will be seen at the deeper areas of the ocean because of the shorter time lapse from the sunlight. In this case, the organisms will not have vertically migrated as much due to the sun setting in a shorter period.

The sampling of the species took place an hour after the sunset, which means that the migration of organisms from the surface would not have gone far. In the event, the sampling was to take place after a longer period the results would be different hence providing the accurate and precise data of which animals’ will be on the surface and which ones will be at the deep ends of the ocean. This sampling in relation to the absence of sunlight could then vary the results gathered in sampling of December 2.

In addition to the element of sunlight or darkness is the factor of the presence of a swell. Notable was the significant difference in the swelling of the waters on the two days the sampling was taking place. On the first day of sampling, the waters were calm, and there was no movement of waters from one point to the next.

On the other hand, the second sampling had a swell of water with considerable movements of water. On December 2nd water was moving in all directions especially in the upwards direction. This movement of water was notable on the boats we were using as it moved in the direction of the water movement.

The movement of water in the ocean determines the positioning of the organisms in the ocean. Some species will exist where and find comfort in still and calm waters and, therefore, when the waters are moving they tend to seek refuge in places where the waters are calm.

This will have an impact on the sampling of species, as there will be a difference of species, not because of the valid reasons, but because of the temporary factor of rough waters. Therefore, this could have been a significant factor, which had an effect on the difference in the sampling of the species (Atsatt and Seapyan 89).

There is also the element of errors, which may have occurred in the sampling of the species. In this case, we will discuss the sources of errors in the sampling, which may have led to the variation of the results. In the two days in which the sampling took place, there was a difference in the IKMTs’ deeper depths.

On September 28 2001, the day trawl took place at 750m, and the night trawl was at 850m. On the other hand, on December 2 2011, both day and night trawl made use of 100m and 400m depths in sampling the species. It is evident that the sampling of data at different depths could be the main source of error in this study. In addition, we performed all the trawls in the San Pedro Basin without having the latitude and longitude coordinates of the first IKMT in September.

We did not even consider this while carrying out the second sampling on December 2. From this, we can deduce that another source of error in the sampling was from the different locations in which the sampling took place.

The quantities of the species in use, in the second sampling, were not recorded making the data less accurate because there is no sense of biomass within the sampled data. Lastly, the under or over abundance of certain species can dictate the presence of other species, and this could have been another source of error in the sampling Hillebrand 53).


In conclusion, the above analysis of the study of species in water is a clear indication of biodiversity in organisms. A latitudinal variety gradient in plank tonic marine bacteria is evident whose existence is subject to various factors. The notable factors, which will determine, the types of species present in the given area are the location, the presence of other species, presence of sunlight or its absence, and the condition of the ocean waters.

From the sampling outcomes, there were certain species, which were present, in day sampling in both days while those which were observed in the night. Although the data collect, may not be accurate the slight difference in the data was due to time factors and seasonality. The temperatures may have been another element, which contributed to the variance because the two days had different temperatures. Another notable difference came from the swelling of the waters, which was because of the movements in day two of the sampling.

Works Cited

Atsatt, Linet and Seapyan, Richard. Analysis of Sampling Variability in Replicated Midwater Trawls off Southern California. California: University of California, 1974. Print.

Christopher, Martin and Lowe Christopher. Assemblage Structure of Fish at Offshore Petroleum Platforms on the San Pedro Shelf of Southern California. New York: American Fisheries Society, 2010. Print.

Hillebrand, Hillson. On the generality of the latitudinal diversity gradient. New York: Am Nat, 2004. Print.

Fenchel, Thatcher. (2004). The ubiquity of small species; Patterns of local and global diversity. New York: Cengage Learning.

Mittelbach, Gibbs. Evolution and the latitudinal diversity gradient: extinction, Speciation and biogeography. London: Ecol Lett, 2007. Print.

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